Systems and methods for optimizing thermal efficiency of a compressed air energy storage system

ABSTRACT

Systems, methods and devices for optimizing thermal efficiency within a gas compression system are described herein. In some embodiments, a device can include a first hydraulic cylinder, a second hydraulic cylinder, and a hydraulic actuator. The first hydraulic cylinder has a first working piston disposed therein for reciprocating movement in the first hydraulic cylinder and which divides the first hydraulic cylinder into a first hydraulic chamber and a second hydraulic chamber. The second hydraulic cylinder has a second working piston disposed therein for reciprocating movement in the second hydraulic cylinder and which divides the second hydraulic cylinder into a third hydraulic chamber and a fourth hydraulic chamber. The hydraulic actuator can be coupled to the first or second working piston, and is operable to move the first and second working pistons in a first direction and a second direction such that volume in the hydraulic chambers are reduced accordingly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/294,862, filed Nov. 11, 2011, and entitled “Systems and Methods forOptimizing Thermal Efficiency of a Compressed Air Energy StorageSystem,” and is related to U.S. patent application Ser. No. 13/294,675,filed Nov. 11, 2011, and entitled “Systems and Methods for Compressingand/or Expanding a Gas Utilizing a Bi-Directional Piston and HydraulicActuator,” the disclosures of which are hereby incorporated by referencein their entireties.

BACKGROUND

The invention relates generally to systems, devices and methods for thecompression and/or expansion of a gas, such as air, and particularly toa system, device and method for optimizing the energy efficiency of acompressed air energy storage system.

Traditionally, electric power plants have been sized to accommodate peakpower demand. Moreover, electric power plant sizing must take intoaccount their maximum power output, minimum power output, and a middlepower output range within which they most efficiently convert fuel intoelectricity. Electric power plants are also constrained in terms of howquickly they can start-up and shut-down, and it is commonly infeasibleto completely shut-down a power plant. The combination of power outputconstraints, and start-up and shut-down constraints, restricts a powerplant's ability to optimally meet a fluctuating power demand. Theserestrictions may lead to increased green house gas emissions, increasedoverall fuel consumption, and/or to potentially higher operating costs,among other drawbacks. Augmenting a power plant with an energy storagesystem may create an ability to store power for later use, which mayallow a power plant to fulfill fluctuating consumer demand in a fashionthat minimizes these drawbacks.

An energy storage system may improve overall operating costs,reliability, and/or emissions profiles for electric power plants.Existing energy storage technologies, however, have drawbacks. By way ofexample, batteries, flywheels, capacitors and fuel cells may providefast response times and may be helpful to compensate for temporaryblackouts, but have limited energy storage capabilities and may becostly to implement. Installations of other larger capacity systems,such as pumped hydro systems, require particular geological formationsthat might not be available at all locations.

Intermittent electric power production sites, such as some wind farms,may have capacities that exceed transmission capabilities. Absentsuitable energy storage systems, such intermittent power productionsites may not be capable of operating at full capacity. The applicantshave appreciated that intermittent production sites may benefit from astorage system that may be sized to store energy, when the productionsite is capable of producing energy at rates higher than may betransmitted. The energy that is stored may be released through thetransmission lines when power produced by the intermittent site is lowerthan transmission line capacity.

Electric power consumption sites, such as buildings, towns, cities,commercial facilities, military facilities, may have consumption thatperiodically exceeds electricity transmission capabilities. Absentsuitable energy storage systems, such power consumers may not be capableof operating at preferred levels. The applicants have appreciated thattransmission constrained consumption sites may benefit from a storagesystem that may be sized to store energy, when the consumption site isconsuming energy at rates lower than may be transmitted, and that thetransmitted energy that is not immediately consumed may be stored. Theenergy that is stored may be released to the consumers when powerconsumption of the consumers is higher than the transmission linecapacity. The energy may also be stored during off-peak time periods(e.g., at night) when electricity prices are generally less expensiveand released during peak time periods (e.g., during the day) whenelectricity prices are generally more expensive.

Compressed air energy storage systems (CAES) are another known type ofsystem in limited use for storing energy in the form of compressed air.CAES systems may be used to store energy, in the form of compressed air,when electricity demand is low, typically during the night, and then torelease the energy when demand is high, typically during the day. Suchsystems include a compressor that operates, often at a constant speed,to compress air for storage. Turbines, separate from the compressor, aretypically used to expand compressed air to produce electricity.Turbines, however, often require the compressed air to be provided at arelatively constant pressure, such as around 35 atmospheres.Additionally or alternatively, air at pressures higher than 35atmospheres may need to be throttled prior to expansion in the turbine,causing losses that reduce the efficiency of the system, and/or reducethe energy density that a storage structure may accommodate.Additionally, to increase electrical energy produced per unit of airexpanded through the turbine, compressed air in such systems is oftenpre-heated to elevated temperatures (e.g., 1000° C.) prior to expansionby burning fossil fuels that both increases the cost of energy from thesystem and produces emissions associated with the storage of energy.

Known CAES-type systems for storing energy as compressed air have amulti-stage compressor that may include intercoolers that cool airbetween stages of compression and/or after-coolers that cool air aftercompression. In such a system, however, the air may still achievesubstantial temperatures during each stage of compression, prior tobeing cooled, which will introduce inefficiencies in the system. Thus,there is a need to provide for CAES type systems that have improvedefficiencies.

A CAES system may be implemented using a hydraulic drive systemcomprised of hydraulic components including components such as hydraulicpumps used to drive working pistons. Therefore, there is also a need forsystems and methods to obtain a high efficiency output of a compressedair energy storage system, or other systems used to compress and/orexpand gas, including controls and operating modes that leveragebi-directional piston movement during operation of such a system.

SUMMARY OF THE INVENTION

Systems, methods and devices for optimizing energy efficiency within adevice or system used to compress and/or expand a gas, such as air, aredescribed herein. In some embodiments, a compressed gas-based energystorage system can include a first hydraulic cylinder, a secondhydraulic cylinder, and a hydraulic actuator. The first hydrauliccylinder has a first working piston disposed therein for reciprocatingmovement in the first hydraulic cylinder and which divides the firsthydraulic cylinder into a first hydraulic chamber and a second hydraulicchamber. The second hydraulic cylinder has a second working pistondisposed therein for reciprocating movement in the second hydrauliccylinder and which divides the second hydraulic cylinder into a thirdhydraulic chamber and a fourth hydraulic chamber. A connecting rod isdisposed between, and coupled to, the first working piston and thesecond working piston. The hydraulic actuator is coupled to at least oneof the first working piston, the second working piston, or theconnecting rod, and is operable to move the first and second workingpistons in a first direction to reduce the volume of the first hydraulicchamber and the third hydraulic chamber, and to move the first andsecond working pistons in a second direction, opposite the firstdirection, to reduce the volume of the second hydraulic chamber and thefourth hydraulic chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a compression and/or expansionsystem according to an embodiment.

FIG. 2 is a schematic illustration of a compressed gas-based energystorage and recovery system, according to an embodiment.

FIG. 3 is a schematic illustration of a compressed gas-based energystorage and recovery system, according to an embodiment.

FIGS. 4A-4D are schematic illustrations of a lock pump used in acompressed gas-based energy storage and recovery system shown in afirst, second, third and fourth configuration, respectively, accordingto an embodiment.

FIGS. 5A-5G are schematic illustrations of a compressed gas-based energystorage and recovery system shown in a first, second, third, fourth,fifth, sixth and seventh configuration, respectively, illustrating acompression cycle according to an embodiment.

FIGS. 6A-6G are schematic illustrations of the compressed gas-basedenergy storage and recovery system of FIGS. 5A-5G shown in a first,second, third, fourth, fifth, sixth and seventh configuration,respectively, illustrating an expansion cycle according to anembodiment.

DETAILED DESCRIPTION

Systems, devices and methods for optimizing and efficiency operating agas compression and/or expansion system are disclosed herein. The gascompression and/or expansion systems can include one or moredouble-acting working pistons movably disposed within a cylinder tocompress gas within a working chamber and configured to compress gaswhen moved in more than one direction. For example, the double-actingpiston can be configured to compress gas both when moved in a firstdirection and when moved in a second direction opposite to the firstdirection. The gas compression and/or expansion systems can also includeone or more double-acting working pistons movably disposed within acylinder and configured to displace liquid within a working chamber whenmoved in more than one direction. For example, the double acting pistoncan be configured to discharge liquid from a first working chamber anddraw liquid into a second working chamber when moved in a firstdirection, and discharge liquid from the second working chamber and drawliquid into the first working chamber when moved in a second direction,opposite the first direction. As used herein the term “piston” is notlimited to pistons of circular cross-section, but can include pistonswith a cross-section of a triangular, rectangular, or other multi-sidedshape. The gas compression and/or expansion systems can be configuredfor two or more stages of gas compression and/or expansion.

In some embodiments, the double-acting working piston within a gascompression and/or expansion system can be driven by or drive one ormore hydraulic actuators. The hydraulic loads applied to the workingpiston(s) can be varied during a given cycle of the system. For example,by applying hydraulic fluid pressure to different hydraulic pistons,and/or different surfaces of the piston(s) within the hydraulicactuator(s), the ratio of the net working surface area of the hydraulicactuator to the working surface area of the working piston acting on thegas and/or liquid in the working chamber can be varied, and thereforethe ratio of the hydraulic fluid pressure to the gas and/or fluidpressure in the working chamber can be varied during a given cycle orstroke of the system. In addition, the number of working pistons/workingchambers and hydraulic actuator can be varied as well as the number ofpiston area ratio changes within a given cycle.

In some embodiments, an actuator can include one or more pump systems,such as for example, one or more hydraulic pumps that can be use to moveone or more fluids within the actuators. U.S. Provisional App. No.61/216,942, to Ingersoll, et al., filed May 22, 2009, entitled“Compressor and/or Expander Device,” and U.S. patent application Ser.Nos. 12/785,086, 12/785,093 and 12/785,100, each filed May 21, 2010 andentitled “Compressor and/or Expander Device” (collectively referred toherein as the “the Compressor and/or Expander Device applications”), thedisclosures of which are hereby incorporated herein by reference, intheir entireties, describe various energy compression and/or expansionsystems in which the systems and methods described herein can beemployed.

The hydraulic actuator can be coupleable to a hydraulic pump, which canhave efficient operating ranges that can vary as a function of, forexample, flow rate and pressure, among other parameters. Systems andmethods of operating the hydraulic pumps/motors to allow them tofunction at an optimal efficiency throughout the stroke or cycle of thegas compression and/or expansion system are described in U.S. patentapplication Ser. No. 12/977,724 to Ingersoll, et al., filed Dec. 23,2010, entitled “Systems and Methods for Optimizing Efficiency of aHydraulically Actuated System,” (“the '724 application”) the disclosureof which is incorporated herein by reference in its entirety.

In some embodiments, the devices and systems described herein can beconfigured for use only as a compressor. For example, in someembodiments, a compressor device described herein can be used as acompressor in a natural gas pipeline, a natural gas storage compressor,or any other industrial application that requires compression of a gas.In another example, a compressor device described herein can be used forcompressing carbon dioxide. For example, carbon dioxide can becompressed in a process for use in enhanced oil recovery or for use incarbon sequestration. In another example, a compressor device describedherein can be used for compressing air. For example, compressed air canbe used in numerous applications which may include cleaningapplications, motive applications, ventilation applications, airseparation applications, cooling applications, amongst others.

In some embodiments, the devices and systems described herein can beconfigured for use only as an expansion device. For example, anexpansion device as described herein can be used to generateelectricity. In some embodiments, an expansion device as describedherein can be used in a natural gas transmission and distributionsystem. For example, at the intersection of a high pressure (e.g., 500psi) transmission system and a low pressure (e.g., 50 psi) distributionsystem, energy can be released where the pressure is stepped down fromthe high pressure to a low pressure. An expansion device as describedherein can use the pressure drop to generate electricity. In otherembodiments, an expansion device as described herein can be used inother gas systems to harness the energy from high to low pressureregulation.

FIG. 1 schematically illustrates a compression and/or expansion device(also referred to herein as “compression/expansion device”) according toan embodiment. A compression/expansion device 100 can include one ormore pneumatic cylinders 110, 130, one or more pistons 120, 140, atleast one actuator 172, a controller 170, and a liquid management system192. The compression/expansion device 100 can be used, for example, in aCAES system.

The piston 120 (referred to herein as “first piston”) is configured tobe at least partially and movably disposed in the first pneumaticcylinder 110. The first piston 120 divides the first pneumatic cylinder110 into, and defines therewith, a first pneumatic chamber and a secondpneumatic chamber (not shown in FIG. 1). The first piston 120 can alsobe coupled to the actuator 172 via a piston rod (not shown in FIG. 1).The actuator 172 can be, for example, an electric motor or ahydraulically driven actuator such as, for example, the hydraulicactuators described in the '724 application, incorporated by referenceabove. The actuator 172 can be used to move the first piston 120 backand forth within the first pneumatic cylinder 110. As the first piston120 moves back and forth within the first pneumatic cylinder 110, avolume of the first pneumatic chamber and a volume of the secondpneumatic chamber will each change. For example, the first piston 120can be moved between a first position in which the first pneumaticchamber has a volume greater than a volume of the second pneumaticchamber, and a second position in which the second pneumatic chamber hasa volume greater than a volume of the first pneumatic chamber.

The piston 140 (referred to herein as “second piston”) is configured tobe at least partially disposed in the second pneumatic cylinder 130. Thesecond piston divides the second pneumatic cylinder into, and definestherewith, a third pneumatic chamber and a fourth pneumatic chamber (notshown in FIG. 1). The second piston 140 can also be coupled to theactuator 172 via a piston rod (not shown in FIG. 1). The actuator 172can be used to move the second piston 140 back and forth within thesecond pneumatic cylinder 130. As the second piston 140 moves back andforth within the second pneumatic cylinder 130, a volume of the thirdpneumatic chamber and a volume of the fourth pneumatic chamber will eachchange. For example, the second piston 140 can be moved between a firstposition in which the third pneumatic chamber has a volume greater thana volume of the fourth pneumatic chamber, and a second position in whichthe fourth pneumatic chamber has a volume greater than a volume of thethird pneumatic chamber.

Each piston 120, 140 can be moved within its respective pneumaticcylinder 110, 130 to compress and/or expand a gas, such as air, withinthe cylinder. In some embodiments, the compression/expansion device 100can be configured to be double-acting, in that at least one of thepistons 120, 140 can be actuated in two directions. In other words, thepistons 120, 140 can be actuated to compress and/or expand gas (e.g.,air) in two directions. For example, in some embodiments, as the firstpiston 120 is moved in a first direction, a first volume of gas having afirst pressure disposed in the first pneumatic chamber of the firstpneumatic cylinder 110 can be compressed by one side of the first piston120 to a second pressure greater than the first pressure, and a secondvolume of gas having a third pressure can enter the second pneumaticchamber on the other side of the first piston 120. When the first piston120 is moved in a second direction opposite the first direction, thesecond volume of gas within the second pneumatic chamber can becompressed by the first piston 120 to a fourth pressure greater than thethird pressure, and simultaneously a third volume of gas can enter thefirst pneumatic chamber. The second piston 140 can be similarly operablewith respect to the third and fourth pneumatic chambers of the secondpneumatic cylinder 130.

As such, movement of the first and second pistons 120, 140 (e.g., by theactuator 172) within each of the first and second pneumatic cylinders110, 130, respectively, can change the volume of the first and secondpneumatic chambers and the third and fourth pneumatic chambers,respectively (e.g., by decreasing the volume to compress the gas, byincreasing the volume as the gas expands). The controller 170 isconfigured to control distribution of an input of hydraulic power, whichcan then be used to drive the actuator 172, such as when thecompression/expansion device 100 is operating to compress gas (i.e., acompression mode). The controller 170 can also be configured to controldistribution of hydraulic power to a pump/motor (not shown in FIG. 1),where the hydraulic power can be converted into mechanical power, suchas when the compression/expansion device 100 is operating to expand agas (i.e., an expansion mode).

In use, the compression/expansion device 100 operates in the compressionmode to compress gas during at least a first stage of compression, inwhich the gas is compressed to a first pressure greater than an initialpressure, and a second stage of compression, in which the gas iscompressed to a second pressure greater than the first pressure.Similarly, the compression/expansion device 100 can operate in theexpansion mode to expand gas during at least a first stage of expansion,in which the gas is permitted to expand to a first pressure lower thanthe pressure of the gas in storage, and a second stage of expansion, inwhich the gas is permitted to expand to a second pressure lower than thefirst pressure.

Each of the first pneumatic cylinder 110 and second pneumatic cylinder130 can include one or more inlet/outlet conduits (not shown in FIG. 1)in fluid communication with their respective pneumatic chambers. Thepneumatic chambers can contain at various time periods during acompression and/or expansion cycle, a quantity of gas (e.g., air) thatcan be communicated to and from the pneumatic chambers via theinlet/outlet conduits. The compression/expansion device 100 can alsoinclude multiple valves (not shown in FIG. 1) coupled to theinlet/outlet conduits and/or to the pneumatic cylinders 110, 130. Thevalves can be configured to operatively open and close the fluidcommunication to and from the pneumatic chambers. Examples of use ofsuch valves are described in more detail in the Compressor and/orExpander Device applications incorporated by reference above.

The liquid management system 192 is configured to control a temperatureof gas as it is compressed and/or expanded within thecompression/expansion device 100 by selectively introducing a liquidinto and/or removing a liquid from the pneumatic cylinders. The liquidcan directly or indirectly receive heat energy from, or release heatenergy to, gas in the pneumatic cylinders. For example, the liquidmanagement system 192 can be configured to receive heat energy from, andthereby lower the temperature of, the gas when the compression/expansiondevice 100 is operating in the compression mode. In another example, theliquid management system 192 can be configured to release heat energyto, and thereby increase the temperature of, the gas when thecompression/expansion device 100 is operating in the expansion mode. Insome embodiments, the liquid management system 192 is configured tocontrol the temperature of gas using a heavy gas (or other suitablesubstance) in addition to using liquid. In other embodiments, however,the liquid management system 192 uses heavy gas (or another suitablesubstance) in lieu of using liquid.

The liquid management system 192 is configured to be coupled to at leastone of the first pneumatic cylinder 110 and the second pneumaticcylinder 130. The liquid management system 192 can include one or morefluid inlet/outlet conduits (not shown in FIG. 1) in fluid communicationwith one or more of the inlet/outlet conduits (not shown in FIG. 1) ofthe first pneumatic cylinder 110 and/or second pneumatic cylinder 130.The liquid management system 192 can also include multiple valves (notshown in FIG. 1) coupled to the inlet/outlet conduits and/or to one ormore chambers (not shown in FIG. 1) of the liquid management system 192.The valves can be configured to operatively open and close the fluidcommunication to and from the liquid management system. Examples of useof such valves are described in more detail in the Compressor and/orExpander Device applications incorporated by reference above.

In some embodiments, the liquid management system can include a lockpump or other device that facilitates movement of liquid into and/or outof the pneumatic cylinders 110, 130 during operation of thecompression/expansion device 100. Examples of lock pumps are illustratedand described with respect to FIGS. 4A-4D. Examples of devices andmethods for optimizing heat transfer within a compression and/orexpansion device are described in more detail in U.S. patent applicationSer. No. 12/977,679 to Ingersoll, et al., filed Dec. 23, 2010, entitled“Methods and Devices for Optimizing Heat Transfer Within a Compressionand/or Expansion Device” (“the '679 application”), incorporated hereinby reference in its entirety.

FIG. 2 is a schematic illustration of an embodiment of an energy storageand recovery system 200 in which a compression/expansion device 201 maybe used to both store energy and release energy that has previously beenstored. Generally, as shown in FIG. 2, a source of electrical power, inthis case a wind farm 208 including a plurality of wind turbines 209,may be used to harvest and convert wind energy to electric energy fordelivery to a motor/generator 278. It is to be appreciated that thesystem 200 may be used with electric sources other than wind farms, suchas, for example, with an electric power grid 206 or solar power sources(not shown). The motor/generator 278 converts the input electrical powerfrom the wind turbines or other sources into mechanical power. Thatmechanical power can then be converted by a hydraulic pump/motor 271into a hydraulic power. In turn, a hydraulic controller 270 controlsdistribution of the hydraulic power to drive one or more hydraulicactuators 272, 274 connected to the compression/expansion device 201.

Energy can be stored within the system 200 in the form of compressedgas, which can be expanded at a later time period to release the energypreviously stored. To store energy generated by the wind farm 208, thehydraulic actuators 272, 274 can change the volume of respectivepneumatic chambers 212, 214, 232, 234, as described in more detailherein. The reduction in volume compresses a gas contained therein.During this process, heat can be removed from the gas. Duringcompression, the gas is delivered to a downstream stage of thecompression/expansion device 201 and eventually, at an elevatedpressure, to a compressed gas storage chamber 204. At a subsequent time,for example, when there is a relatively high demand for power on thepower grid 206, and/or when energy prices are high, compressed gas maybe communicated from the storage chamber 204 and expanded through thecompression/expansion device 201. Expansion of the compressed gas drivesthe hydraulic actuators 272, 274, which, in turn, displace fluid togenerate hydraulic power. The hydraulic controller 270 directs thehydraulic power to the pump/motor 271, which converts the hydraulicpower to mechanical power. In turn, the motor/generator 278 converts themechanical power to electrical power for delivery to the power grid 206.During this process, heat can be added to the gas.

The compression/expansion device 201, as illustrated in FIG. 2, includesa first pneumatic cylinder 210, a second pneumatic cylinder 230, thefirst actuator 272 operatively coupled to the first pneumatic cylindervia a first working piston 220, the second actuator 274 operativelycoupled to the second pneumatic cylinder via a second working piston240, and the hydraulic controller 270 operatively coupled to the firstand second actuators 272, 274.

The first pneumatic cylinder 210 is configured for a first stage of gascompression. The first pneumatic cylinder 210 has the first workingpiston 220 disposed therein for reciprocating movement in the firstpneumatic cylinder. The first working piston 220 divides the firstpneumatic cylinder 210 into, and thereby defines, a first pneumaticchamber 212 and a second pneumatic chamber 214. The first pneumaticcylinder 210 is fluidically coupleable to the gas source. The firstpneumatic chamber 212 includes a first fluid port 216 and a second fluidport 218. The second pneumatic chamber 214 includes a first fluid port222 and a second fluid port 224. The first fluid port 216 of the firstpneumatic chamber 212 and the first fluid port 222 of the secondpneumatic chamber 214 are each fluidically couplable to a source of gas202. The gas source 202 can be, for example, atmospheric air or apre-compressor.

The second pneumatic cylinder 230 is configured for a second stage ofgas compression. The second pneumatic cylinder 230 has the secondworking piston 240 disposed therein for reciprocating movement in thesecond pneumatic cylinder. The second working piston 240 divides thesecond pneumatic cylinder 230 into, and thereby defines, a thirdpneumatic chamber 232 and a fourth pneumatic chamber 234. The third andfourth pneumatic chambers 232, 234 of the second pneumatic cylinder 230have a collective volume less than a collective volume of the first andsecond pneumatic chambers 212, 214 of the first pneumatic cylinder 210.Additionally, a maximum volume of each of the third and fourth pneumaticchambers 232, 234 is less than a maximum volume of each of the first andsecond pneumatic chambers 212, 214.

The third pneumatic chamber 232 includes a first fluid port 236 and asecond fluid port 238. The fourth pneumatic chamber 234 includes a firstfluid port 242 and a second fluid port 244. The second pneumaticcylinder 230 is configured to be fluidically coupleable to the firstpneumatic cylinder 210. Specifically, the first fluid port 236 of thethird pneumatic chamber 232 is configured to be fluidically coupleableto the second fluid port 218 of the first pneumatic chamber 212. In thismanner, gas can be communicated from the first pneumatic chamber 212 viathe fluid ports 218, 236 into the third pneumatic chamber 232.Additionally, the first fluid port 242 of the fourth pneumatic chamber234 is configured to be fluidically coupleable to the second fluid port224 of the second pneumatic chamber 214. In this manner, gas can becommunicated from the second pneumatic chamber 214 via the fluid ports224, 242 into the fourth pneumatic chamber 234.

The second pneumatic cylinder 230 is configured to be fluidicallycoupleable to the compressed gas storage chamber 204. Specifically, thesecond fluid port 238 of the third pneumatic chamber 232 is fluidicallycoupleable to the gas storage chamber, and the second fluid port 244 ofthe fourth pneumatic chamber 234 is fluidically coupleable to thecompressed gas storage chamber 204.

As noted above, each of the first working piston 220 and the secondworking piston 240 are configured for reciprocating movement in thefirst pneumatic cylinder 210 and the second pneumatic cylinder 230,respectively. The first working piston 220 is coupled to the firsthydraulic actuator 272, and the second working piston 220 is coupled tothe second hydraulic actuator 274. The first hydraulic actuator 272 andthe second hydraulic actuator 274 are each fluidically coupleable to thehydraulic controller 270.

The hydraulic controller is operable in a compression mode in which gasis discharged from the second pneumatic cylinder 230 to the compressedgas storage chamber at a higher pressure than it enters the firstpneumatic cylinder 210 from the gas source 202. In the compression mode,the hydraulic controller 270 is configured to produce a hydraulicactuator force via the first hydraulic actuator 272 on the first workingpiston 220. Such hydraulic actuator force is sufficient to move thefirst working piston 220 in a first direction such that gas contained inthe first pneumatic chamber 212 is discharged from the first pneumaticchamber into the third pneumatic chamber 232. The hydraulic actuatorforce is also sufficient to move the first working piston 220 in asecond direction, opposite the first direction, such that gas containedin the second pneumatic chamber 214 is discharged from the secondpneumatic chamber into the fourth pneumatic chamber 234. In thecompression mode, the hydraulic controller 270 is also configured toproduce a hydraulic actuator force via the second hydraulic actuator 274on the second working piston 240. Such hydraulic actuator force issufficient to move the second working piston 240 in a first directionsuch that gas contained in the third pneumatic chamber 232 is dischargedfrom the third pneumatic chamber into the compressed gas storage chamber204. The hydraulic actuator force is also sufficient to move the secondworking piston 220 in a second direction, opposite the first direction,such that gas contained in the fourth pneumatic chamber 234 isdischarged from the fourth pneumatic chamber into the compressed gasstorage chamber 204.

The hydraulic controller is also operable in an expansion mode in whichgas is discharged from the first pneumatic cylinder 210 to the gassource at a lower pressure than it enters the second pneumatic cylinder230 from the compressed gas storage chamber 204. In the expansion mode,gas can be transferred from the storage chamber 204 into the secondpneumatic cylinder 230, and, when gas expands in at least one of thethird pneumatic chamber 232 and the fourth pneumatic chamber 234 of thesecond pneumatic cylinder 230, the gas exerts a force on the secondworking piston 240, thereby moving the second working piston in one ofthe first direction and the second direction. When the second workingpiston 240 is moved by the expanding gas, the second working piston isconfigured to produce a hydraulic actuator force via the secondhydraulic actuator 274, i.e. to do work on the second hydraulic actuator274. The hydraulic controller 270 controls distribution of the work doneon the hydraulic actuator to the pump/motor 271, where the work can beconverted into mechanical power, which can then be converted intoelectrical power by the motor/generator 278.

Similarly, in the expansion mode, gas can be transferred from the firststage of expansion in the second pneumatic cylinder 230 into the firstpneumatic cylinder 210 for a second stage of expansion. When gas expandsin at least one of the first pneumatic chamber 212 or the secondpneumatic chamber 214 of the first pneumatic cylinder 210, the gasexerts a force on the first working piston 220, thereby moving the firstworking piston in one of the first direction or the second direction.When the first working piston 220 is moved by the expanding gas, thefirst working piston 220 is configured to produce a hydraulic actuatorforce via the first hydraulic actuator 272, i.e. to do work on the firsthydraulic actuator 272. The hydraulic controller 270 controlsdistribution of the work done on the hydraulic actuator to thepump/motor 271, where the work can be converted into mechanical power,which can then be converted into electrical power by the motor/generator278.

The compression/expansion device 201 can include one or more valves tocontrol the flow of gas between the gas source 202 and the compressedgas storage chamber 204. For example, a first valve 280 can beconfigured to selectively permit the gas to flow between the gas source202 and the first pneumatic chamber 212. Similarly, a second valve 282can be configured to selectively permit the gas to flow between the gassource 202 and the second pneumatic chamber 214. A third valve 284 and afourth valve 286 can be configured to selectively permit the flow of gasbetween the first pneumatic chamber 212 and the third pneumatic chamber232 and between the second pneumatic chamber 214 and the fourthpneumatic chamber 234, respectively. A fifth valve 288 is configured toselectively control the flow of gas between the third pneumatic chamber232 and the compressed gas storage chamber 204. Similarly, a sixth valve290 is configured to selectively control the flow of gas between thefourth pneumatic chamber 234 and the compressed gas storage chamber 204.

In use, the energy storage and recovery system 200, and thecompression/expansion system 201 particularly, is configured to operatein the compression mode to compress gas for storage. As noted above,wind energy can be harvested by the wind turbines 209 of the wind farm208 and converted by the wind turbines into electric power for deliveryto the motor/generator 278. The motor/generator 278 inputs theelectrical power into the pump/motor 271 where it is converted intohydraulic power. The hydraulic controller 270 controls distribution,such as using appropriate software and/or a system of valves, of thehydraulic power to actuate each of the first hydraulic actuator 272 andthe second hydraulic actuator 274. Upon actuation, the first hydraulicactuator 272 moves the first working piston 220 within the firstpneumatic cylinder 210 in the first direction. As the first workingpiston 220 is moved in the first direction, gas contained in the firstpneumatic chamber 212 is discharged from the first pneumatic chamber viaits second fluid port 218 into the third pneumatic chamber 232 via itsfirst fluid port 236. Upon actuation, the second hydraulic actuator 274moves the second working piston 240 within the second pneumatic cylinder230 in the second direction. As the second working piston 240 is movedin the second direction, gas contained in the fourth pneumatic chamber234 is discharged from the fourth pneumatic chamber via its second fluidport 244 to the compressed gas storage chamber 204.

Upon further actuation of the first hydraulic actuator 272, the firsthydraulic actuator 272 moves the first working piston 220 within thefirst pneumatic cylinder 210 in the second direction. As the firstworking piston 220 is moved in the second direction, gas contained inthe second pneumatic chamber 214 is discharged from the second pneumaticchamber via its second fluid port 224 into the fourth pneumatic chamber234 via its first fluid port 242. Upon further actuation of the secondhydraulic actuator 274, the second hydraulic actuator moves the secondworking piston 240 within the second pneumatic cylinder 230 in the firstdirection. As the second working piston 240 is moved in the firstdirection, gas contained in the third pneumatic chamber 232 isdischarged from the third pneumatic chamber via its second fluid port238 to the compressed gas storage chamber 204. In this manner, thesecond working piston 240 can be characterized as moving out of phasewith the first working piston 220. In some embodiments, movement of thefirst working piston 240 in the first direction is substantiallyconcurrent with movement of the second working piston 220 in the seconddirection, and vice versa. The compressed gas is then stored in thecompressed gas storage chamber 204.

In use, the energy storage and recovery system 200, and thecompression/expansion system 201 particularly, are also configured tooperate in the expansion mode to expand compressed gas (e.g., togenerate electrical energy). In the expansion mode, compressed gas ispermitted to flow from the compressed gas storage chamber 204 into thefourth pneumatic chamber 234 of the second pneumatic cylinder 230. Asthe gas expands in the fourth pneumatic chamber 234, the gas exerts aforce on the second working piston 240 to move the second working pistonin the first direction, thereby increasing the volume of the fourthpneumatic chamber 234 and decreasing the volume of the third pneumaticchamber 232. Movement of the second working piston 240 in the firstdirection causes the second hydraulic actuator 274 to displace a firstvolume of hydraulic fluid. When the second working piston 240 is movedin the first direction, gas contained in the third pneumatic chamber 232is displaced to the first pneumatic chamber 212. In the first pneumaticchamber 212, the displaced gas expands and exerts a force on the firstworking piston 220 to move the first working piston in the seconddirection, thereby increasing the volume of the first pneumatic chamber212 and decreasing the volume of the second pneumatic chamber 214.Movement of the first working piston 220 in the first direction causesthe first hydraulic actuator 272 to displace a second volume ofhydraulic fluid. When the first working piston 220 is moved in thesecond direction, gas contained in the second pneumatic chamber 214 isdisplaced from the second pneumatic chamber to the gas source 202.

In the expansion mode, gas is also permitted to flow from the compressedgas storage chamber 204 into the third pneumatic chamber 232 of thesecond pneumatic cylinder 230. As the gas expands in the third pneumaticchamber 232, the gas exerts a force on the second working piston 240 tomove the second working piston in the second direction, therebyincreasing the volume of the third pneumatic chamber 232 and decreasingthe volume of the fourth pneumatic chamber 234. Movement of the secondworking piston 240 in the second direction causes the second hydraulicactuator 274 to displace a third volume of hydraulic fluid. When thesecond working piston 240 is moved in the second direction, gascontained in the fourth pneumatic chamber 234 is displaced to the secondpneumatic chamber 214. In the second pneumatic chamber 214, thedisplaced gas expands and exerts a force on the first working piston 220to move the first working piston in the first direction, therebyincreasing the volume of the second pneumatic chamber and decreasing thevolume of the first pneumatic chamber 212. Movement of the first workingpiston 220 in the second direction causes the first hydraulic actuator272 to displace a fourth volume of hydraulic fluid. When the firstworking piston 220 is moved in the first direction, gas contained in thefirst pneumatic chamber 212 is displaced from the first pneumaticchamber to the gas source 202.

The displacement of each of the first and third volumes of fluid by thesecond actuator 274 and of the second and fourth volumes of fluid by thefirst actuator 272 generates hydraulic power which the hydrauliccontroller 270 directs to the pump/motor 271, where the hydraulic poweris converted to mechanical power. The motor/generator 278 is configuredto convert the mechanical power to electrical power, which can bedelivered to the electric power grid 206 for consumption.

A compression/expansion device 300 according to an embodiment isillustrated in FIG. 3. The device 300 includes a first pneumaticcylinder 310 divided into a first pneumatic chamber 312 and a secondpneumatic chamber 314 by a first working piston 320. The first workingpiston 320 is coupled to a first hydraulic actuator 372, which isfluidically coupleable to a hydraulic controller 370. The hydrauliccontroller 370 is configured to control distribution of a hydraulicforce or power from a pump/motor 371 to the first hydraulic actuator 372and a second hydraulic actuator 374, described below. The pump/motor 371is configured to convert mechanical power received from amotor/generator 378 into hydraulic power, and to convert hydraulic powerinto mechanical power to be transferred to the motor/generator. Themotor/generator 378 is configured to convert mechanical power intoelectrical power, and to convert electrical power into mechanical power.

The first and second pneumatic chambers 312, 314 of the first pneumaticcylinder 310 are fluidically coupleable to a gas source 302. Gas fromthe gas source can be introduced into the first pneumatic chamber 312via a first fluid port 316 of the first pneumatic chamber and into thesecond pneumatic chamber 314 via a first fluid port 322 of the secondpneumatic chamber. Flow of gas between the gas source 302 and the firstand second pneumatic chambers 312, 314 can be selectively controlledwith valves 380, 382, respectively.

The device 300 includes a second pneumatic cylinder 330 divided into athird pneumatic chamber 332 and a fourth pneumatic chamber 334 by asecond working piston 340. The second working piston 340 is coupled tothe second hydraulic actuator 374, which is fluidically coupleable tothe hydraulic controller 370. The third and fourth pneumatic chambers332, 334 of the second pneumatic cylinder 330 have a collective volumeless than a collective volume of the first and second pneumatic chambers312, 314 of the first pneumatic cylinder 310. Additionally, a maximumvolume of each of the third and fourth pneumatic chambers 332, 334 isless than a maximum volume of each of the first and second pneumaticchambers 312, 314.

The first pneumatic chamber 312 is fluidically couplable to the thirdpneumatic chamber 332. Specifically, gas can be permitted to flow out ofa second fluid port 318 of the first pneumatic chamber 312 and into thethird pneumatic chamber 332 via a first fluid port 336 of the thirdpneumatic chamber. Gas can also be permitted to flow out of a secondfluid port 324 of the second pneumatic chamber 314 and into the fourthpneumatic chamber 334 via a first fluid port 342 of the fourth pneumaticchamber. Flow of gas between the first and third pneumatic chambers 312,332 can be selectively controlled with valve 384, and flow of gasbetween the second and fourth pneumatic chambers 314, 334 can beselectively controlled with valve 386.

The third and fourth pneumatic chambers 332, 334 are fluidicallycoupleable to a compressed gas storage chamber 304. Specifically, gascan flow between the third pneumatic chamber 332 via a second fluid port338 of the third pneumatic chamber and the compressed gas storagechamber 34, and between the fourth pneumatic chamber 334 via a secondfluid port 344 of the fourth pneumatic chamber and the compressed gasstorage chamber 304. Flow of gas between the third and fourth pneumaticchambers 332, 334 and the compressed gas storage chamber 304 can beselectively controlled with valves 388, 390, respectively.

The device 300 can be similar in many respects to thecompression/expansion devices described herein (e.g.,compression/expansion device 100, compression/expansion device 201) andincludes components similar in many respects to similarly identifiedcomponents of such devices. Additionally, the device 300 is similar inoperation to compress and/or expand a gas, as described above withrespect to devices 100, 201. The device 300 also includes a liquidmanagement system 392. The liquid management system 392 is fluidicallycoupleable with the first and second pneumatic chambers 312, 314 of thefirst pneumatic cylinder 310 and with the third and fourth pneumaticchamber 332, 334 of the second pneumatic cylinder 330. As such, theliquid management system 392 is configured to transfer a heat transferfluid (e.g., a liquid or a heavy gas) to and/or from each pneumaticchamber 312, 314, 332, 334.

Flow of the heat transfer fluid (e.g., water) between the liquidmanagement system 392 and the first and second pneumatic chambers 312,314 can be selectively controlled by valves 394, 395, respectively. Flowof the heat transfer fluid between the liquid management system 392 andthe third and fourth pneumatic chambers 332, 334 can be selectivelycontrolled by valves 396, 397, respectively. In this manner, the liquidmanagement system 392 is configured to change or otherwise control atemperature of gas as it is compressed and/or expanded within thecompression/expansion device 300. For example, the liquid managementsystem 392 can be configured to lower the temperature of the gas, suchas when the compression/expansion device 300 is operating in thecompression mode, for example, by transferring heat transfer fluid intoat least one of the pneumatic chambers 312, 314, 332, 334 such that theheat transfer fluid can cool or otherwise draw heat away from gascontained within the respective pneumatic chamber.

In another example, the liquid management system 392 can be configuredto increase the temperature of the gas, such as when thecompression/expansion device 300 is operating in the expansion mode, forexample, by transferring heat transfer fluid into at least one of thepneumatic chambers 312, 314, 332, 334 such that the heat transfer fluidcan increase the heat of gas contained within the respective pneumaticchamber. Examples of devices and methods for optimizing heat transferwithin a compression and/or expansion device are described in moredetail in the '679 application incorporated by reference above.

In some embodiments, the liquid management system 392 is configured totransfer heat transfer fluid to and/or from the pneumatic chambers 312,314, 332, 334 using a lock pump (not shown in FIG. 3). For example,FIGS. 4A-4C illustrate a lock pump 490 that can be part of a liquidmanagement system for transferring heat energy to and/or from acompression/expansion device. The lock pump 490 is shown in FIGS. 4A-4Cin a first, second and third configuration, respectively. The lock pump490 includes a first hydraulic cylinder 450, a second hydraulic cylinder460, a first working piston 451, a second working piston 461, a pistonrod 477, and an actuator 476.

The first and second hydraulic cylinders 450, 460 are each configured tocontain fluid capable of absorbing and/or releasing heat, such as water,carbon dioxide, calcium chloride, brine, glycol and/or the like. Suchfluid is also referred to herein as “heat transfer fluid.” The firsthydraulic cylinder 450 can be fluidically isolated from the secondhydraulic cylinder 460 such that any heat transfer fluid containedwithin the first hydraulic cylinder 450 is prevented from flowing intothe second hydraulic cylinder 460 and vice versa. The first hydrauliccylinder 450 can also be thermally isolated from the second hydrauliccylinder 460 so that each cylinder 450, 460 can contain and/or maintainfluid at a specific temperature irrespective of the temperature of fluidin the other cylinder. For example, the first hydraulic cylinder 450 canmaintain fluid at 10 degrees Celsius and the second hydraulic cylinder460 can maintain fluid at 60 degrees Celsius without affecting thetemperature of the cooler fluid in the first hydraulic cylinder 450. Thefirst hydraulic cylinder 450 can be separated (or isolated) from thesecond hydraulic cylinder 460 by a divider (not identified in FIGS.4A-4C) such as, for example, a wall or other like barrier. In thisexample, the first hydraulic cylinder 450 and the second hydrauliccylinder 460 can be formed from a single cylindrical structure where thedivider creates the boundaries of the cylinders 450, 460. In someembodiments, the first hydraulic cylinder 450 and the second hydrauliccylinder 460 can be separately formed structures that can be coupledtogether or, alternatively, spaced apart from each other. Although thefirst and second hydraulic cylinders 450, 460 are illustrated as beingsubstantially the same size and shape, in other embodiments, the sizeand/or shape of each hydraulic cylinder 450, 460 can differ. Forexample, in some embodiments, the volume of the first hydraulic cylinder450 can be greater than the volume of the second hydraulic cylinder 460.

The first working piston 451 is configured to be at least partially andmovably disposed in the first hydraulic cylinder 450. The first workingpiston 451 divides the first hydraulic cylinder 450 into, and definestherewith, a first hydraulic chamber 452 and a second hydraulic chamber454. The first working piston 451 is coupled to the actuator 476 via thepiston rod 477. The actuator 476 can be, for example, an electric motoror a hydraulically driven actuator such as, for example, the hydraulicactuators described in the '724 application, incorporated by referenceabove. The actuator 476 can be used to move the first working piston 451back and forth within the first hydraulic cylinder 450.

The second working piston 461 is configured to be at least partiallydisposed in the second hydraulic cylinder 460. The second working piston461 divides the second hydraulic cylinder 460 into, and definestherewith, a third hydraulic chamber 462 and a fourth hydraulic chamber462. The second working piston 461 is coupled to the actuator 476 viathe piston rod 477. As such, the second working piston 461 isoperatively coupled to, and moveable with, the first working piston 451.The actuator 476, therefore, can be used to move the second workingpiston 461 back and forth within the second hydraulic cylinder 460 atthe same time the first working piston 451 is moved back and forthwithin the first hydraulic chamber 450. In other words, the first andsecond working pistons 451, 461 operate or move “in phase” with eachother. This in-phase movement is illustrated and described below withrespect to FIGS. 4A-4C. In other embodiments, the actuator 476 can beconfigured to move the first and second working pistons 451, 461 backand forth within their respective cylinders at different times such thatthe respective movement of the first and second working pistons 451, 461is “out of phase.”

As shown in FIG. 4A, the first working piston 451 and the second workingpiston 461 are in a first (or starting) position at or towards the endof their respective hydraulic cylinders 450, 460. The first workingpiston 451 is disposed within the first hydraulic cylinder 450 such thatthe volume of the first hydraulic chamber 452 is less than the volume ofthe second hydraulic chamber 454. In some embodiments, the first workingpiston 451 is disposed within the first hydraulic cylinder 450 such thatthe volume of the first hydraulic chamber 452 is at or near zero. Inother embodiments, the first hydraulic chamber 452 can have a differentminimum volume.

The second working piston 461 is disposed within the second hydrauliccylinder 460 such that the volume of the third hydraulic chamber 462 isless than the volume of the fourth hydraulic chamber 464. In someembodiments, the second working piston 461 is disposed within the secondhydraulic cylinder 460 such that the volume of the third hydraulicchamber 462 is at or near zero. In other embodiments, the thirdhydraulic chamber 462 can have a different minimum volume.

As shown in FIG. 4A, the volume of the first hydraulic chamber 452 issubstantially equal to the volume of the third hydraulic chamber 462,and the volume of the second hydraulic chamber 454 is substantiallyequal to the volume of the fourth hydraulic chamber 464. In someembodiments, the volume of two or more of these chambers 452, 454, 462,464 are not equal (or substantially equal) and can vary depending on thestructure of the lock pump 490 and/or the specific needs of the system.For example, in some embodiments, the second working piston 461 iscoupled to the piston rod 477 and the second working piston 461 isdisposed within the second hydraulic cylinder 460 such that the volumeof the third hydraulic chamber 462 is greater than the volume of thefirst hydraulic chamber 452. In some embodiments, the size of the firsthydraulic cylinder 450 differs from the size of the second hydrauliccylinder 460 such that the volumes of their respective chambers differ.In some instances, however, despite the size differences between thehydraulic cylinders 450, 460, the volume of the first hydraulic chamber452 can still be substantially equal to the volume of the thirdhydraulic cylinder 462 due to the placement of the pistons 451, 461within their respective hydraulic cylinders 450, 460.

In FIG. 4B, the first working piston 451 and the second working piston461 are shown in a second, intermediate, position between the firstposition and third position. The first working piston 451 is disposedwithin the first hydraulic cylinder 450 such that the volume of thefirst and second hydraulic chambers 452, 454 are substantially equal,and the second working piston 461 is disposed within the first hydrauliccylinder 460 such that the volume of the third and fourth hydraulicchambers 462, 464 are also substantially equal. In some embodiments,however, the first and second hydraulic chambers 452, 454 can havedifferent volumes, and/or the third and fourth hydraulic chambers 462,464 can have different volumes.

The first and second working pistons 451, 461 are moved from the firstposition to the second position by the actuator 476. Specifically, theactuator 476 moves the first working piston 451 in a first directiontowards an opposing end of the first hydraulic cylinder 450 whilesimultaneously moving the second working piston 461 in the firstdirection towards an opposing end of the second hydraulic cylinder 460.Since the first working piston 451 is operatively coupled to the secondworking piston 461 via the piston rod 477, the actuator 476 need onlyapply a force to one of the pistons 451, 461 to move the set of pistons451, 461. In other words, moving the first working piston 451 in thefirst direction results in the second working piston 461 moving in thefirst direction. The distance that the first working piston 451 moveswithin the first hydraulic cylinder 450 is substantially equal to thedistance that the second working piston 461 moves within the secondhydraulic cylinder 460.

Movement of the pistons 451, 461 from the first position to the secondposition results in the volume of the first and third hydraulic chambers452, 462 increasing and the volume of the second and fourth hydraulicchambers 454, 464 decreasing. Therefore, in the second position, thefirst and third hydraulic chambers 452, 462 are capable of containingmore fluid than previously allowed in the first position, and the secondand fourth hydraulic chambers 454, 464 are not capable of containing asmuch fluid as previously allowed in the first position. During operationof the lock pump 490 and as the pistons 451, 461 transition from thefirst position to the second position, additional fluid can be drawninto the first and third hydraulic chambers 452, 462 from an externalsource such as a pond, pool or tank, and fluid within the second andfourth hydraulic chambers 454, 464 can be discharged or expelled fromthe second and fourth hydraulic chambers 454, 464 to, for example, thecompressor/expander device. As will be discussed in more detail herein,it is possible that fluid entering the hydraulic chambers 452, 462 canproduce sufficient hydraulic force to move the pistons 451, 461. In thismanner, the pistons 451, 461 can be moved by both the actuator 476 andhydraulic force.

In FIG. 4C, the first working piston 451 and the second working piston461 are shown in a third (or final) position at or towards the opposingend of their respective hydraulic cylinders 450, 460. Movement of thefirst working piston 451 from its first position to its third positioncompletes a first stroke of the first working piston 451. Likewise, thedistance the second working piston 461 moves from its first position toits third position completes a first stroke of the second working piston461. Since the first and second working pistons 451, 461 are operativelymoveable together, these first strokes can be collectively referred toherein as a first stroke of the lock pump 490.

As shown in FIG. 4C, the first working piston 451 is disposed within thefirst hydraulic cylinder 450 such that the volume of the first hydraulicchamber 452 is greater than the volume of the second hydraulic chamber454. In some embodiments, the first working piston 451 is disposedwithin the first hydraulic cylinder 450 such that the volume of thesecond hydraulic chamber 454 is at or near zero. In other embodiments,the second hydraulic chamber 454 can have a different minimum volume.

The second working piston 461 is disposed within the second hydrauliccylinder 460 such that the volume of the third hydraulic chamber 462 isgreater than the volume of the fourth hydraulic chamber 464. In someembodiments, the second working piston 461 is disposed within the secondhydraulic cylinder 460 such that the volume of the fourth hydraulicchamber 464 is at or near zero. In other embodiments, the fourthhydraulic chamber 464 can have a different minimum volume.

In FIG. 4C, the first working piston 451 is disposed within the firsthydraulic cylinder 450 such that the volume of the first and secondhydraulic chambers 452, 454 are substantially equal, and the secondworking piston 461 is disposed within the first hydraulic cylinder 460such that the volume of the third and fourth hydraulic chambers 462, 464are also substantially equal. In some embodiments, however, the firstand second hydraulic chambers 452, 454 can have different volumes,and/or the third and fourth hydraulic chambers 462, 464 can havedifferent volumes.

The first and second working pistons 451, 461 are moved from the secondposition to the third position by the actuator 476. Specifically, theactuator 476 continues moving the first working piston 451 in the firstdirection towards the opposing end of the first hydraulic cylinder 450while simultaneously moving the second working piston 461 in the firstdirection towards the opposing end of the second hydraulic cylinder 460.Movement of the pistons 451, 461 from the second position to the thirdposition results in the volume of the first and third hydraulic chambers452, 462 increasing further and the volume of the second and fourthhydraulic chambers 454, 464 decreasing further. In the third position,the first and third hydraulic chambers 452, 462 are capable ofcontaining more fluid than previously allowed in the first and secondpositions. In other words, the first and third hydraulic chambers 452,462 are at their maximum volume in the third position and can thereforecontain a maximum amount of fluid. To account for this increase involume, additional fluid can be drawn into the first and/or thirdhydraulic chambers 452, 462. In contrast, when the second and fourthhydraulic chambers 454, 464 are in the third position, they are notcapable of containing as much fluid as in the first and secondpositions. In other words, the second and fourth hydraulic chambers 454,464 are at their minimum volume in the third position and, therefore,can only contain a minimum amount of fluid. To account for this decreasein volume, fluid can be discharged or expelled from the second andfourth hydraulic chambers 454, 464.

Although the lock pump 490 is illustrated and described as having asingle actuator 476 for moving the first and second working pistons 451,461, in other embodiments, the lock pump 490 can include two actuators.For example, the first actuator and the second actuator can beoperatively coupled to the first and second working pistons 451, 461,respectively, via piston rods. In this manner, the first actuator can,for example, exert a force on the first working piston 451 to move thefirst and second working pistons 451, 461 in the first direction, andthe second actuator can, for example, exert a force on the secondworking piston 461 to move the first and second working pistons 451, 461in a second (or opposite) direction. In other embodiments, a firstactuator (e.g., actuator 476) can be operatively coupled to the firstworking piston 451 via a first piston rod (e.g., piston rod 477) and asecond actuator can be separately and operatively coupled to the secondworking piston 461 via a second piston rod. In this manner, movement ofthe first working piston 451 can be independent from movement of thesecond working piston 461. In this manner, the timing and/or distance tocomplete a stoke for the first working piston 451 can be different fromthe timing and/or distance required for the second working piston 461 tocomplete a stroke. The respective movement of the pistons 451, 461 cantherefore be “out of phase.”

Although the lock pump 490 is illustrated and described as having twohydraulic cylinders 450, 460, in other embodiments, the lock pump 490can any include any number of hydraulic cylinders. The lock pump 490 caninclude, for example, one hydraulic cylinder or more than two hydrauliccylinders. FIG. 4D is a schematic illustration of a lock pump 690 havingthree hydraulic cylinders 680, 650, 660. The lock pump 690 also includesthree working pistons 681, 651, 661, a piston rod 677, and an actuator676. In some embodiments, however, the lock pump 690 does not includethe actuator 676. The first and second hydraulic cylinders 650, 660 andtheir respective chambers 652, 654, 662, 664 and pistons 651, 661operate similar to the hydraulic cylinders 450, 460 and chambers 452,454, 462, 464 and pistons 451, 461 shown in FIGS. 4A-4C and, therefore,are not described in detail herein. The actuator 676 operates similar tothe actuator 476 shown in FIGS. 4A-4C and, therefore, is also notdescribed in detail herein.

The third hydraulic cylinder 680 is configured to contain heat transferfluid. In some embodiments, the third hydraulic cylinder 680 can containa different type of heat transfer fluid from the first and/or secondhydraulic cylinders 650, 660. For example, the third hydraulic cylinder680 can contain a heavy gas, such as carbon dioxide, while the first andsecond hydraulic cylinders 650, 660 contain a liquid, such as water. Thethird hydraulic cylinder 680 can be fluidically isolated from the firsthydraulic cylinder 650 and, in some embodiments, the third hydrauliccylinder 680 can also be thermally isolated from the first hydrauliccylinder 650. The third hydraulic cylinder 680 can be separated (orisolated) from the first hydraulic cylinder 650 by a divider (notidentified in FIG. 4D) such as, for example, a wall or other likebarrier. The hydraulic cylinders 680, 650, 660 can be formed from asingle cylindrical structure where dividers create the boundaries of thecylinders 680, 650, 660. In some embodiments, the first, second, and/orthird hydraulic cylinders 680, 650, 660 can be separately formedstructures that can be coupled together or, alternatively, spaced apartfrom each other. For example, the first and second hydraulic cylinders650, 660 can be formed from a single structure and the third hydrauliccylinder 680 is a separately formed structure that is coupled to thefirst hydraulic cylinder 650. The first, second, and third hydrauliccylinders 680, 650, 660 can have any suitable shape and/or size relativeto each other.

The third working piston 681 operates similar to the first and secondworking pistons 651, 661. More specifically, the third working piston681 is configured to be at least partially and movably disposed in thethird hydraulic cylinder 680, thereby dividing the third hydrauliccylinder 680 into a fifth hydraulic chamber 682 and a sixth hydraulicchamber 684. The third working piston 681 is coupled to the actuator 676via the piston rod 677. In this manner, the all three working pistons681, 651, 661 are operatively coupled together and move simultaneouslywithin their respective cylinders 680, 650, 660 in the same mannerdescribed above with respect to pistons 451, 461. In some embodiments,less than all the pistons 681, 651, 661 operate in phase with eachother. In some embodiments, one or more of the pistons 681, 651, 661operate out of phase with another piston.

The third working piston 681 is configured to move within the thirdhydraulic cylinder 680 between various positions. For example, the thirdworking piston 681 is illustrated in FIG. 4D in the same position as thepistons 451, 461 shown in FIG. 4C—i.e., in a third (or final) position.The third working piston 681 can move from this position back to thesecond position and the first position in the same manner as the pistons451, 461 shown in FIGS. 4A and 4B. Moving the third working piston 681between these positions results in a change of the volume of the fifthand sixth hydraulic chambers 682, 684. In some embodiments, the thirdworking piston 681 moves or is otherwise disposed within the thirdhydraulic cylinder 680 such that the volume of the fifth hydraulicchamber 682 is substantially equal to the volume of the first and thirdhydraulic chambers 652, 662. In other embodiments, the third workingpiston 681 moves or is otherwise disposed within the third hydrauliccylinder 680 such that the volume of the fifth hydraulic chamber 682 isdifferent from the first and/or third hydraulic chambers 652, 662.

Referring to FIGS. 5A-5G, a compression/expansion device 500 accordingto an embodiment is configured for inclusion in a system for storingenergy and for releasing energy that has previously been stored.Specifically, the compression/expansion device 500 is configured tocompress gas for storage and to expand gas that has previously beencompressed. As will be discussed in more detail herein, the device 500is coupled to a liquid management system 592 that transfers fluid to andfrom the device 500 during the compression and expansion processes tooptimize the thermal efficiency of the device 500. The liquid managementsystem 592 can be similar in many respects to the liquid managementsystems described herein (e.g., liquid management system 192, and liquidmanagement system 392) and includes components similar in many respectsto similarly identified components of such systems (e.g., lock pump490). The device 500 can be similar in many respects to thecompression/expansion devices described herein (e.g.,compression/expansion device 100, compression/expansion device 201,compression/expansion device 300) and includes components similar inmany respects to similarly identified components of such devices.Details regarding the structure and operation of the device 500 are alsodescribed in a related application having Attorney Docket No.GCOM-012/00US 312615-2042, entitled “Systems and Methods for Compressingand/or Expanding a Gas Utilizing a Bi-Directional Piston and HydraulicActuator,” which is incorporated by reference herein in its entirety.

The device 500 includes a first pneumatic cylinder 510 divided into afirst pneumatic chamber 512 and a second pneumatic chamber 514 by afirst working pneumatic piston 520. The first working pneumatic piston520 is coupled to a first hydraulic actuator 572, which is fluidicallycoupleable to a hydraulic controller 570. The first and second pneumaticchambers 512, 514 of the first pneumatic cylinder 510 are fluidicallycoupleable to a gas source 502. Gas from the gas source can beintroduced into the first pneumatic chamber 512 via a first fluid port516 of the first pneumatic chamber 512 and into the second pneumaticchamber 514 via a first fluid port 522 of the second pneumatic chamber514. Flow of gas between the gas source 502 and the first and secondpneumatic chambers 512, 514 can be selectively controlled with valves580, 582, respectively.

The first and second pneumatic chambers 512, 514 of the first pneumaticcylinder 510 are each fluidically coupleable to the liquid managementsystem 592, and more particularly, to a lock pump 590 of the liquidmanagement system 592. As will be described in more detail herein, fluidfrom the lock pump 590 can be introduced into the first pneumaticchamber 512 via a second fluid port 511 of the first pneumatic chamber512 and into the second pneumatic chamber 514 via a second fluid port515 of the second pneumatic chamber 514. Flow of fluid between the lockpump 590 and the first and second pneumatic chambers 512, 514 can beselectively controlled with valves 594, 595, respectively.

The device 500 includes a second pneumatic cylinder 530 divided into athird pneumatic chamber 532 and a fourth pneumatic chamber 534 by asecond working pneumatic piston 540. The second working pneumatic piston540 is coupled to a second hydraulic actuator 574, which is fluidicallycoupleable to the hydraulic controller 570. The third and fourthpneumatic chambers 532, 534 of the second pneumatic cylinder 530 have acollective volume less than a collective volume of the first and secondpneumatic chambers 512, 514 of the first pneumatic cylinder 510.Additionally, a maximum volume of each of the third and fourth pneumaticchambers 532, 534 is less than a maximum volume of each of the first andsecond pneumatic chambers 512, 514.

The first pneumatic chamber 512 is fluidically couplable to the thirdpneumatic chamber 532. Specifically, fluids can be permitted to flowbetween a third fluid port 518 of the first pneumatic chamber 512 and afirst fluid port 536 of the third pneumatic chamber 532. Fluids can alsobe permitted to flow between a third fluid port 524 of the secondpneumatic chamber 514 and a first fluid port 542 of the fourth pneumaticchamber 534. Flow of fluid between the first and third pneumaticchambers 512, 532 can be selectively controlled with valve 584, and flowof fluid between the second and fourth pneumatic chambers 514, 534 canbe selectively controlled with valve 586.

The third and fourth pneumatic chambers 532, 534 are each fluidicallycoupleable to the lock pump 590 of the liquid management system 592. Aswill be described in more detail herein, fluid from the lock pump 590can be introduced into the third pneumatic chamber 532 via a secondfluid port 531 of the third pneumatic chamber 532 and into the fourthpneumatic chamber 534 via a second fluid port 535 of the fourthpneumatic chamber 534. Flow of fluid between the lock pump 590 and thethird and fourth pneumatic chambers 532, 534 can be selectivelycontrolled with valves 596, 597, respectively.

The third and fourth pneumatic chambers 532, 534 are also eachfluidically coupleable to a compressed gas storage chamber 504.Specifically, gas can flow between the third pneumatic chamber 532 via athird fluid port 538 of the third pneumatic chamber 532 and thecompressed gas storage chamber 504, and between the fourth pneumaticchamber 534 via a third fluid port 545 of the fourth pneumatic chamber534 and the compressed gas storage chamber 504. Flow of gas between thethird and fourth pneumatic chambers 532, 534 and the compressed gasstorage chamber 504 can be selectively controlled with valves 588, 590,respectively.

The liquid management system 592 includes the lock pump 590 and a liquidstorage structure 575. The lock pump 590 includes a first hydrauliccylinder 550 divided into a first hydraulic chamber 552 and a secondhydraulic chamber 554 by a first working hydraulic piston 551. The firstworking hydraulic piston 551 is coupled to a third hydraulic actuator576, which is fluidically coupleable to the hydraulic controller 570.The first and second hydraulic chambers 552, 554 of the first hydrauliccylinder 550 are each fluidically coupleable to the liquid storagestructure 575. The liquid storage structure 575 can be one or moresuitable fluid reservoirs suitable for storing heat transfer fluid, suchas, for example, a pond, a pool, a tank, an underground storage vessel,an aboveground storage vessel and/or the like. Fluid (i.e., heattransfer fluid) from the liquid storage structure 575 can be introducedinto the first hydraulic chamber 552 via a first fluid port 543 of thefirst hydraulic chamber 552 and into the second hydraulic chamber 554via a first fluid port 547 of the second hydraulic chamber 554. Flow offluid between the liquid storage structure 575 and the first and secondhydraulic chambers 552, 554 can be selectively controlled with valves591, 593, respectively.

The first hydraulic chamber 552 of the first hydraulic cylinder 550 isfluidically coupleable to the first pneumatic chamber 512 of the firstpneumatic cylinder 510, and the second hydraulic chamber 554 of thefirst hydraulic cylinder 550 is fluidically coupleable to the secondpneumatic chamber 514 of the first pneumatic cylinder 510. Specifically,fluid can be permitted to flow between a second fluid port 513 of thefirst hydraulic chamber 552 and the second fluid port 511 of the firstpneumatic chamber 512. Fluids can be permitted to flow between a secondfluid port 517 of the second hydraulic chamber 554 and the second fluidport 515 of the second pneumatic chamber 514. Flow of fluid between thefirst hydraulic chamber 552 and the first pneumatic chamber 512 can beselectively controlled with valve 594, and flow of fluid between thesecond hydraulic chamber 554 and the second pneumatic chamber 514 can beselectively controlled with valve 595.

The lock pump 590 includes a second hydraulic cylinder 560 divided intoa third hydraulic chamber 562 and a fourth hydraulic chamber 564 by asecond working hydraulic piston 561. The second working hydraulic piston561 is coupled to the third hydraulic actuator 576. As such, the secondworking hydraulic piston 561 is operatively coupled to, and moveablewith, the first working piston 551. The third and fourth hydraulicchambers 562, 564 of the second hydraulic cylinder 560 are also eachfluidically coupleable to the liquid storage structure 575. Fluid fromthe liquid storage structure 575 can be introduced into the thirdhydraulic chamber 562 via a first fluid port 527 of the third hydraulicchamber 562 and into the fourth hydraulic chamber 564 via a first fluidport 523 of the fourth hydraulic chamber 564. Flow of fluid between theliquid storage structure 575 and the third and fourth hydraulic chambers562, 564 can be selectively controlled with valves 598, 599,respectively.

The third hydraulic chamber 562 of the second hydraulic cylinder 560 isfluidically coupleable to the fourth pneumatic chamber 534 of the secondpneumatic cylinder 530, and the fourth hydraulic chamber 564 of thesecond hydraulic cylinder 560 is fluidically coupleable to the thirdpneumatic chamber 534 of the second pneumatic cylinder 530.Specifically, fluid can be permitted to flow between a second fluid port537 of the third hydraulic chamber 562 and the second fluid port 535 ofthe fourth pneumatic chamber 534. Fluids can be permitted to flowbetween a second fluid port 533 of the fourth hydraulic chamber 564 andthe second fluid port 531 of the third pneumatic chamber 532. Flow offluid between the third hydraulic chamber 562 and the fourth pneumaticchamber 534 can be selectively controlled with valve 597, and flow offluid between the fourth hydraulic chamber 564 and the third pneumaticchamber 532 can be selectively controlled with valve 596.

Referring to FIGS. 5A-5G, the compression/expansion device 500 isillustrated in first, second, third, fourth, fifth, sixth, and seventhconfigurations, respectively, of a compression mode or cycle. As shownin FIG. 5A, in the first configuration, each valve 580, 582, 584, 586,588, 590, 591, 593, 594, 595, 596, 597, 598, 599 is closed. The firstworking pneumatic piston 520 is in a first (or starting) position at ortowards an end of the first pneumatic cylinder 510 such that the volumeof the first pneumatic chamber 512 is less than the volume of the secondpneumatic chamber 514. In some embodiments, when the first workingpneumatic piston 520 is in its first position, the first working pistonis disposed within the first pneumatic cylinder 510 such that the volumeof the first pneumatic chamber 512 is at or near zero. In otherembodiments, the first pneumatic chamber 512 can have a differentminimum volume. In some embodiments, a first mass of gas at a firstpressure is contained in the second pneumatic chamber 514.

The second working pneumatic piston 540 is in a first (or starting)position at or towards an end of the second pneumatic cylinder 530 suchthat the volume of the third pneumatic chamber 532 is greater than thevolume of the fourth pneumatic chamber 534. In some embodiments, whenthe second working pneumatic piston 540 is in its first position, thesecond working pneumatic piston 540 is disposed within the secondpneumatic cylinder 530 such that the volume of the fourth pneumaticchamber 534 is at or near zero. In other embodiments, the fourthpneumatic chamber 534 is configured to have a different minimum volume.A second mass of gas at a second pressure is contained in the thirdpneumatic chamber 534.

The first and second working hydraulic pistons 551, 561 are in a first(or starting) position at or towards an end of their respectivehydraulic cylinders 550, 560 such that the volume of the second andfourth hydraulic chambers 554, 564 are greater than the volume of thefirst and third hydraulic chambers 552, 562. In some embodiments, whenthe first working hydraulic piston 551 is in its first position, thehydraulic piston 551 is disposed within the first hydraulic cylinder 550such that the volume of the first hydraulic chamber 552 is at or nearzero. In some such embodiments, the second working hydraulic piston 561is also in its first position and disposed within the second hydrauliccylinder 560 such that the volume of the third hydraulic chamber 562 isat or near zero. In other embodiments, the first hydraulic chamber 552and/or the third hydraulic chamber 562 are configured to have differentminimum volumes. In some embodiments, the hydraulic chambers containheat transfer fluid, such as water.

Turning now to FIG. 5B, the valves 580, 586, 588, 591, 595, 597, 599 areopened. At valve 591, the liquid storage structure 575 is fluidicallycoupled to the first hydraulic chamber 552 such that a first volume ofliquid can flow from the liquid storage structure 575 into the firsthydraulic chamber 552 via the first fluid port 543. The first workinghydraulic piston 551 is moved by the third hydraulic actuator 576 in afirst direction towards an opposing end of the first hydraulic cylinder550, thereby increasing the volume of the first hydraulic chamber 552and reducing the volume of the second hydraulic chamber 554.

As shown in FIG. 5B, the first working hydraulic piston 551 is in asecond position (i.e., a first intermediate position) between its firstposition and its final, fourth position at or towards the end of theopposing end of the first hydraulic cylinder 550. Movement of the firstworking hydraulic piston 551 the distance from its first position to itsfourth position completes a first stroke of the first working hydraulicpiston 551. While moving in the first direction from its first positionto its second position, the first working hydraulic piston 551 operatesto draw a first volume of liquid from the liquid storage structure 575into the first hydraulic chamber 552, and discharge a second volume ofliquid from the second hydraulic chamber 554 into the second pneumaticchamber 514 of the first pneumatic cylinder 510. In other words,movement of the first working hydraulic piston 551 in the firstdirection pulls liquid from the liquid storage structure 575 into thefirst hydraulic chamber 552, and pushes (or forces) liquid out of thesecond hydraulic chamber 554 and into the second pneumatic chamber 514.The displacement of liquid into and out of the first and secondhydraulic chambers 552, 554 can be due, in part, to pressure variancesproduced by the movement of the first working hydraulic piston 551 inthe first direction.

At valve 580, the gas source 502 is fluidically coupled to the firstpneumatic chamber 512 such that a third mass of gas at a third pressurecan flow from the gas source 502 into the first pneumatic chamber 512via the first fluid port 516. The first working pneumatic piston 520 ismoved by the first hydraulic actuator 572 in a second direction towardsan opposing end of the first pneumatic cylinder 510, thereby increasingthe volume of the first pneumatic chamber 512 and reducing the volume ofthe second pneumatic chamber 514.

In FIG. 5B, the first working pneumatic piston 520 is shown in a secondposition (i.e., a first intermediate position) between its firstposition and its final, fourth position at or towards the opposing endof the first pneumatic cylinder 510. Movement of the first workingpiston 520 the distance from its first position to its fourth positioncompletes a first stroke of the first working pneumatic piston 520.Movement of the first working pneumatic piston 520 in the seconddirection can occur substantially simultaneously with movement of thefirst working hydraulic piston 551 in the first direction. While movingin the second direction from its first position to its second position,the first working pneumatic piston 520 operates to compress the firstmass of gas contained in the second pneumatic chamber 514, such that thefirst mass of gas is discharged from the second pneumatic chamber 514 tothe fourth pneumatic chamber 534 at a fourth pressure higher than thefirst pressure. The valve 586 between the second pneumatic chamber 514and the fourth pneumatic chamber 534 is opened when the first workingpneumatic piston 520 is moved in its second direction to permit thefirst mass of gas to be discharged from the second pneumatic chamber 514to the fourth pneumatic chamber 534 as it is being compressed.

In some embodiments, the second volume of liquid is introduced into thesecond pneumatic chamber 514 at the same time the first workingpneumatic piston 520 is compressing the first mass of gas. The secondvolume of liquid is preferably a relatively cool or cold liquid that,upon contact with the first mass of gas, cools or lowers the temperatureof the first mass of gas. Specifically, when the liquid enters thesecond pneumatic chamber 514 and contacts the first mass of gas, theheat energy produced during compression of the gas is transferreddirectly to the liquid. At least a portion of the warmed liquid is thenallowed to flow from the second pneumatic chamber 514 to the fourthpneumatic chamber 534 along with the first mass of gas. In someembodiments, the heat energy is transferred to an intermediate structuredisposed in the second pneumatic chamber 514. The intermediate structurecan be, for example, a heat transfer element as described in the '679application, incorporated by reference above. In such embodiments, theheat energy is further transferred from the intermediate structure tothe liquid.

The second working pneumatic piston 540 is moved by the second hydraulicactuator 574 in a third direction, opposite the second direction,towards an opposing end (or top) of the second pneumatic cylinder 530,thereby increasing the volume of the fourth pneumatic chamber 534 andreducing the volume of the third pneumatic chamber 532. Movement of thesecond working pneumatic piston 540 in the third direction can occursubstantially simultaneously with movement of the first workingpneumatic piston 520 in the second direction. The valve 586 between thesecond pneumatic chamber 514 and the fourth pneumatic chamber 534 can beopen while the first hydraulic actuator 572 moves the first workingpneumatic piston 520 in the second direction and while the secondhydraulic actuator 574 moves the second working pneumatic piston 540 inthe third direction. In this manner, the total volume of the secondpneumatic chamber 530 and the fourth pneumatic chamber 534 is reduceddue, in part, to the difference in size between the first pneumaticcylinder 510 and the second cylinder 530.

In FIG. 5B, the second working pneumatic piston 540 is shown in a secondposition (i.e., a first intermediate position) between its firstposition and a final, fourth position at or towards an opposing end ofthe second pneumatic cylinder 530. Movement of the second workingpneumatic piston 540 the distance from its first position to its fourthposition completes a first stroke of the second working piston 540.

While moving in the third direction, the second working pneumatic piston540 operates to compress the second mass of gas contained in the thirdpneumatic chamber 532, such that the second mass of gas is dischargedfrom the third pneumatic chamber 532 to the compressed gas storagechamber 504 at a fifth pressure higher than the second pressure. Asdiscussed above, compression of the second mass of gas results in heatenergy being produced. The valve 588 between the third pneumatic chamber532 and the compressed gas storage chamber 504 is opened when the secondworking pneumatic piston 540 is moving in the third direction to permitthe second mass of gas to be discharged from the third pneumatic chamber532 to the compressed gas storage chamber 504 as it is being compressed.In some embodiments, the third pneumatic chamber 532 contains liquidthat can absorb the heat energy produced by the second mass of gasduring compression so that the second mass of gas is cooled before beingdischarged from the third pneumatic chamber 532 to the compressed gasstorage chamber 504.

As shown in FIG. 5B, the second working hydraulic piston 561 is in asecond position (i.e., a first intermediate position) between its firstposition and its final, fourth position at or towards the end of theopposing end of the second hydraulic cylinder 560. Movement of thesecond working hydraulic piston 561 the distance from its first positionto its fourth position completes a first stroke of the second workinghydraulic piston 561. As discussed above, the second working hydraulicpiston 561 is operatively coupled to the first working hydraulic piston551 such that the first and second working hydraulic pistons 551, 561move in phase, concurrently with each other. The first and secondworking hydraulic pistons 551, 561 move in the same direction andsimultaneously complete strokes. The third hydraulic actuator 576 needonly exert a force on one of the pistons 551, 561 to initiate movementof both of the pistons 551, 561 in a certain direction.

While moving in the first direction from its first position to itssecond position, the second working hydraulic piston 561 operates toreceive a third volume of liquid from the fourth pneumatic chamber 534into the third hydraulic chamber 562, and discharge a fourth volume ofliquid from the fourth hydraulic chamber 564 into the liquid storagestructure 575. In other words, movement of the second working hydraulicpiston 561 in the first direction allows liquid from the fourthpneumatic chamber 534 to be received into the third hydraulic chamber562, and pushes (or forces) liquid out of the fourth hydraulic chamber564 and into the liquid storage structure 575. The displacement ofliquid into and out of the third and fourth hydraulic chambers 562, 564can be due, in part, to pressure differences produced by the movement ofthe second working hydraulic piston 561 in the first direction. Forexample, the pressure in the third hydraulic chamber 562 can be greaterthan the pressure in the fourth pneumatic chamber 534 when the secondworking hydraulic piston 561 is moved in the first direction, thusdisplacing the fourth volume of liquid into the liquid storage structure575. In some embodiments, the lock pump 590 can be located below thepneumatic cylinders #, # such that the third volume of liquid is drawnto the third hydraulic chamber 562 by gravitational forces. In someembodiments, the third volume of liquid includes a portion of the secondvolume of liquid. In other words, some of the second volume of liquidremains within the fourth pneumatic chamber 534 after the second workinghydraulic piston 561 is moved in the first direction. In otherembodiments, however, all of the liquid contained within the fourthpneumatic chamber 534 can be transferred to the third hydraulic chamber562.

As shown in FIG. 5C, the valves 580, 586, 588, 591, 595, 597, 599 remainopen as the pneumatic pistons 520, 540 and the hydraulic pistons 551,561 continue moving in their respective directions. The first workingpneumatic piston 520 is shown in FIG. 5C in a third position (i.e., asecond intermediate position), closer to the opposing end of the firstpneumatic cylinder 510 than it previously was in the second position(i.e., the first intermediate position). Gas and/or fluid continues toflow into and/or out of the first pneumatic cylinder in the same mannerdescribed above with respect to FIG. 5B. The second working pneumaticpiston 540 is also shown in FIG. 5C in a third position (i.e., a secondintermediate position), closer to the opposing end of the secondpneumatic cylinder 530 than it previously was in the second position(i.e., the first intermediate position). Gas and/or fluid also continuesto flow into and/or out of the second pneumatic cylinder 530 in the samemanner described above with respect to FIG. 5B.

Furthermore, the first and second working hydraulic pistons 551, 561 areshown in FIG. 5C in a third position (i.e., a second intermediateposition), closer to the opposing end of the first and second hydrauliccylinders 550, 560, respectively, than they previously were in thesecond position (i.e., the first intermediate position). The first andsecond working hydraulic pistons 551, 561 continue to be moved in thefirst direction by the third hydraulic actuator 576. In someembodiments, the amount of force that the third hydraulic actuator 576exerts on the first and second working hydraulic pistons 551, 561 tomove the first and second working hydraulic pistons 551, 561 is minimal(or nominal). For example, in some embodiments, the third hydraulicactuator 576 only exerts a force sufficient to overcome hydraulic headand frictional losses from fluid flows in the piping. Similarly, valves586, 595, 597 are all open so the pressures in hydraulic chambers 554and 562 and pneumatic chambers 514 and 534 are all equal (ignoring headpressure and frictional losses). Thus, with respect to the lock pump590, the pressure in the second hydraulic chamber 554 is greater thanthe pressure in the first hydraulic chamber 552 and trying to force thefirst working hydraulic piston 551 to the left, and the pressure in thethird hydraulic chamber 562 is greater than the pressure in the fourthhydraulic chamber 564 and trying to force the second working hydraulicpiston 561 to the right. Therefore, the lock pump 590 is balanced andthe third hydraulic actuator 576 can be sized such that it only needs toovercome the frictional losses and/or hydraulic head in order to movethe volumes of liquid around.

In some embodiments, the fluid pressure within one or more of thehydraulic chambers 552, 554, 562, 564 is sufficient to move the firstand second hydraulic pistons 551, 561 in the first direction in lieu ofor in conjunction with the third hydraulic actuator 576. Morespecifically, the fluid pressure that is produced when liquid isintroduced into one or more of the chambers 552, 554, 562, 564 can exerta hydraulic force on the first and/or second hydraulic pistons 551, 561sufficient to move the hydraulic pistons 551, 561. For example, as shownin FIGS. 5B and 5C, the valve 591 between the first hydraulic chamber552 and the liquid storage structure 575, and the valve 599 between thefourth hydraulic chamber 564 and the liquid storage structure 575 areboth in the open position. In an embodiment where the liquid storagestructure 575 is a containment pond opened to the atmosphere, thepressure in the first and fourth hydraulic chambers 552, 564 will beequal (e.g., 1 bar). Similarly, valves 586, 595, 597 are all open so thepressure in the second hydraulic chamber 554, the third hydraulicchamber 562, the second pneumatic chamber 514, and the fourth pneumaticchamber 534 are all substantially equal provided hydraulic headdifferentials and frictional pressure losses are minimal Thus, as thepressure increases in the second and fourth pneumatic chambers 514, 534,the pressure increases in the second and third hydraulic chambers 554,562. The increased pressure in the second hydraulic chamber 554 exerts aforce on the first hydraulic working piston 551 in a fourth direction(opposite the first direction) and the increased pressure in the thirdhydraulic chamber 562 exerts a substantially equal and opposite force onthe second hydraulic working piston 561 in the first direction. In someembodiments, this fluid pressure is the primary force acting on thefirst and second working hydraulic pistons 551, 561 to move thehydraulic pistons 551, 561 and the hydraulic force exerted by the thirdhydraulic actuator 576 can be a secondary force. In this matter, thelock pump 590 can be considered to be balanced during operation of theliquid management system 592 and the actuator 576 can be sized such thatit only needs to overcome any hydraulic head and/or frictional losses inthe system in order to move volumes of liquid between the liquid storagestructure 575 and the compression/expander device 500. In someembodiments, the hydraulic force exerted by the third hydraulic actuator576 can be a primary force and the hydraulic fluid pressure exerted bythe liquid returning from the compressor/expander device 500 is thesecondary force acting on the first and second working hydraulic pistons551, 561.

Referring now to FIG. 5D, the previously-opened valves 580, 586, 588,591, 595, 597, 599 are closed and valves 582, 584, 590, 593, 594, 596,598 are opened. The first working hydraulic piston 551 has completed itsfirst stroke and is in its fourth position, at or proximate to theopposing end of the first hydraulic cylinder 550. As such, the firstworking hydraulic piston 551 is in position to begin its second stroke,in which the first working hydraulic piston 551 is moved the distancefrom its fourth position to its first position. In some embodiments,when the first working hydraulic piston 551 is in its fourth position,the first working hydraulic piston 551 is disposed within the firsthydraulic cylinder 550 such that the volume of the second hydraulicchamber 554 is at or near zero. In other embodiments, the secondhydraulic chamber 554 is configured to have a different minimum volume.

The second working hydraulic piston 561 has also completed its firststroke and is in its fourth position, at or proximate to the opposingend of the second hydraulic cylinder 560. As such, the second workinghydraulic piston 561 is in position to begin its second stroke, in whichthe second working hydraulic piston 561 is moved the distance from itsfourth position to its first position. Here, the first and secondworking hydraulic pistons 551, 561 move the same distance to complete astroke. In some embodiments, when the second working hydraulic piston561 is in its fourth position, the second working hydraulic piston 561is disposed within the second hydraulic cylinder 560 such that thevolume of the fourth hydraulic chamber 564 is at or near zero. In otherembodiments, the fourth hydraulic chamber 564 is configured to have adifferent minimum volume.

In FIG. 5D, the first working pneumatic piston 520 has completed itsfirst stroke and is in its fourth position, at or proximate to theopposing end of the first pneumatic cylinder 510. As such, the firstworking pneumatic piston 520 is in position to begin its second stroke,in which the first working pneumatic piston 520 is moved the distancefrom its fourth position to its first position. In some embodiments,when the first working pneumatic piston 520 is in its fourth position,the first working pneumatic piston 520 is disposed within the firstpneumatic cylinder 510 such that the volume of the second pneumaticchamber 514 is at or near zero. In other embodiments, the secondpneumatic chamber 514 is configured to have a different minimum volume.

The second working pneumatic piston 540 has completed its first strokeand is in its fourth position, at or proximate to the opposing end ofthe second pneumatic cylinder 530. As such, the second working pneumaticpiston 540 is in position to begin its second stroke, in which thesecond working pneumatic piston 540 is moved the distance from itsfourth position to its first position. In some embodiments, when thesecond working pneumatic piston 540 is in its fourth position, thesecond working pneumatic piston 540 is disposed within the secondpneumatic cylinder 530 such that the volume of the third pneumaticchamber 532 is at or near zero. In other embodiments, the thirdpneumatic chamber 532 is configured to have a different minimum volume.

As shown in FIG. 5E, the valves 582, 584, 590, 593, 594, 596, 598 remainopen. At valve 593, the liquid storage structure 575 is fluidicallycoupled to the second hydraulic chamber 554 such that a fifth volume ofliquid can flow from the liquid storage structure 575 into the secondhydraulic chamber 554 via the first fluid port 547. The first workinghydraulic piston 551 is moved by the third hydraulic actuator 576 in afourth direction, opposite the first direction, towards the opposing endof the first hydraulic cylinder 550, thereby increasing the volume ofthe second hydraulic chamber 554 and reducing the volume of the firsthydraulic chamber 552.

As shown in FIG. 5E, the first working hydraulic piston 551 is in thethird position between its fourth position and its first position duringits second stroke. While moving in the fourth direction from its fourthposition back to its third position, the first working hydraulic piston551 operates to draw a fifth volume of liquid from the liquid storagestructure 575 into the second hydraulic chamber 554, and discharge thefirst volume of liquid from the first hydraulic chamber 552 into thefirst pneumatic chamber 512 of the first pneumatic cylinder 510. Inother words, movement of the first working hydraulic piston 551 in thefourth direction pulls liquid from the liquid storage structure 575 intothe second hydraulic chamber 554, and pushes (or forces) liquid out ofthe first hydraulic chamber 552 and into the first pneumatic chamber512.

At valve 582, the gas source 502 is fluidically coupled to the secondpneumatic chamber 514 such that gas is permitted to flow from the gassource 502 into the second pneumatic chamber via its first fluid port522. The first working pneumatic piston 520 is moved by the firsthydraulic actuator 572 in the third direction, thereby increasing thevolume of the second pneumatic chamber 514 and reducing the volume ofthe first pneumatic chamber 512. The first working pneumatic piston 520is shown in its third position during its second stroke. While moving inthe third direction, the first working pneumatic piston 520 operates tocompress the third mass of gas contained in the first pneumatic chamber512, thereby discharging the third mass of gas from the first pneumaticchamber 512 and into the third pneumatic chamber 532 at a sixth pressurehigher than the third pressure. The valve 584 between the firstpneumatic chamber 512 and the third pneumatic chamber 532 can be openwhile the first hydraulic actuator 572 moves the first working pneumaticpiston 520 in the third direction and while the second hydraulicactuator 574 moves the second working pneumatic piston 540 in the seconddirection. In this manner, the total volume of the first pneumaticchamber 512 and the third pneumatic chamber 532 is reduced due, in part,to the difference in size between the first pneumatic cylinder 510 andthe second cylinder 530.

Compression of the third mass of gas produces heat energy and, as aresult, the temperature of the third mass of gas rises unless that heatenergy is removed from the gas during the compression process. In someembodiments, the first volume of liquid is introduced into the firstpneumatic chamber 512 as the third mass of gas is being compressed. Thetemperature of the liquid is relatively cooler than the temperature ofthe gas and, upon contact with the third mass of gas, cools or lowersthe temperature of the gas. Said another way, heat energy produced bythe third mass of gas is transferred directly to the first volume ofliquid when the liquid contacts the gas. At least a portion of thewarmed liquid is then allowed to flow from the first pneumatic chamber512 to the third pneumatic chamber 532 along with the third mass of gas.In some embodiments, the heat energy is transferred to an intermediatestructure disposed in the first pneumatic chamber 512. The intermediatestructure can be, for example, a heat transfer element as described inthe '679 application, incorporated by reference above. In suchembodiments, the heat energy is further transferred from theintermediate structure to the liquid.

The second working pneumatic piston 540 is moved by the second hydraulicactuator 574 in the second direction, thereby increasing the volume ofthe third pneumatic chamber 532 and reducing the volume of the fourthpneumatic chamber 534. Movement of the second working pneumatic piston540 in the second direction can occur substantially simultaneously withmovement of the first working pneumatic piston 520 in the thirddirection. In FIG. 5E, the second working pneumatic piston 540 is shownin its third position during its second stroke. While moving in thesecond direction, the second working pneumatic piston 540 operates tocompress the first mass of gas contained in the fourth pneumatic chamber534, thereby discharging the first mass of gas from the fourth pneumaticchamber 534 to the compressed gas storage chamber 504 a seventh pressurehigher than the fourth pressure.

As discussed above, compression of the first mass of gas results in heatenergy being produced. The valve 590 between the fourth pneumaticchamber 534 and the compressed gas storage chamber 504 is opened whenthe second working pneumatic piston 540 is moving in the seconddirection to allow the first mass of gas to be discharged from thefourth pneumatic chamber 534 to the compressed gas storage chamber 504as it is being compressed. In some embodiments, the fourth pneumaticchamber 534 contains liquid that can absorb the heat energy produced bythe first mass of gas during compression so that the first mass of gasis cooled before being discharged from the fourth pneumatic chamber 534to the compressed gas storage chamber 504.

As shown in FIG. 5E, the second working hydraulic piston 561 is in thethird position during its second stroke. As discussed above, the secondworking hydraulic piston 561 moves with the first working hydraulicpiston 551. Here, the second working hydraulic piston 561 moves in thefourth direction with the first working hydraulic piston 551. Whilemoving in the fourth direction from its fourth position to its thirdposition, the second working hydraulic piston 561 operates to draw asixth volume of liquid (e.g., including at least a portion of the firstvolume of liquid) from the third pneumatic chamber 532 into the fourthhydraulic chamber 564, and discharge the third volume of liquid (e.g.,including at least a portion of the second volume of liquid) from thethird hydraulic chamber 562 into the liquid storage structure 575. Inother words, movement of the second working hydraulic piston 561 in thefourth direction pulls liquid from the third pneumatic chamber 532 intothe fourth hydraulic chamber 564, and pushes (or forces) liquid out ofthe third hydraulic chamber 562 and into the liquid storage structure575. In some embodiments, at least a portion of the first volume ofliquid can remain within the third pneumatic chamber 532 after thesecond working hydraulic piston 561 has completed its second stroke inthe fourth direction. In this manner, the remaining portion of the firstvolume of liquid can be used to cool gas that enters the third pneumaticchamber 532 during the next compression cycle. In other embodiments, thefirst volume of liquid is removed from the third pneumatic chamber 532completely, and transferred to the fourth hydraulic chamber 564. In suchembodiments, the first volume of liquid can be substantially equal tothe sixth volume of liquid.

In some embodiments, the third pneumatic chamber 532 can retain heatenergy produced by another previously compressed mass of gas in additionto the heat energy produced by the third mass of gas. The first volumeof liquid can be configured to absorb the heat energy produced bycompression of a previous mass of gas and the heat energy produced bycompression of the third mass of gas before any portion of the firstvolume of liquid is discharged from the third pneumatic chamber 532. Aswill be discussed in more detail below, this warmed liquid can bere-used during the expansion cycle to warm gas as it expands.

As shown in FIG. 5F, the valves 582, 584, 590, 593, 594, 596, 598 remainopen as the pneumatic pistons 520, 540 and the hydraulic pistons 551,561 continue moving in their respective directions. The first workingpneumatic piston 520 is shown in FIG. 5F in its second position duringits second stroke. Fluids continues to flow into and/or out of the firstpneumatic cylinder 510 in the same manner described above with respectto FIG. 5E. The second working pneumatic piston 540 is also shown inFIG. 5F in its second position during its second stroke. Fluids alsocontinues to flow into and/or out of the second pneumatic cylinder 530in the same manner described above with respect to FIG. 5E.

Furthermore, the first and second working hydraulic pistons 551, 561 areshown in FIG. 5F in their second position during their second stroke.The first and second working hydraulic pistons 551, 561 continue to bemoved in the second direction by the third hydraulic actuator 576. Asdiscussed above, in some embodiments, the amount of force that the thirdhydraulic actuator 576 exerts on the first and second working hydraulicpistons 551, 561 to move the first and second working hydraulic pistons551, 561 is minimal (or nominal). The force exerted by the thirdhydraulic actuator 576 can be sufficient to overcome hydraulic headand/or frictional losses, as previously discussed.

Referring to FIG. 5G, the valves 582, 584, 590, 593, 594, 596, 598,which were previously open, are now closed and the valves 580, 586, 588,591, 595, 597, 599 are reopened. More particularly, the valve 582 isclosed to stop the flow of gas from the gas source 502 to the thirdpneumatic chamber 514. The third mass of gas has been discharged fromthe first pneumatic chamber 512 to the third pneumatic chamber 532 atthe sixth pressure higher than the second pressure, and is contained inthe third pneumatic chamber 532. The valve 584 between the firstpneumatic chamber 512 and the third pneumatic chamber 532 is closed toprevent the third mass of gas from flowing back into the first pneumaticchamber 512 from the third pneumatic chamber 532. The first mass of gashas been discharged from the fourth pneumatic chamber 534 to thecompressed gas storage chamber 504 at the seventh pressure higher thanthe fourth pressure. The valve 590 between the fourth pneumatic chamber534 and the compressed gas storage chamber 504 is closed to prevent thefirst mass of gas from flowing back into the fourth pneumatic chamber534 from the storage chamber 504. Valves 580, 586, 588, 591, 595, 597,599 are opened to permit the compression cycle to be continued orrepeated.

As noted above, when a mass of gas is transferred into a pneumaticchamber (e.g., first, second, third, or fourth pneumatic chambers 512,514, 532, 534, respectively), the valve (e.g., valve 580, 582, 584, 586,respectively) associated with the inlet port (e.g., port 516, 522, 536,542, respectively) is closed to prevent backwards flow of the gas duringcompression. Additionally, the valve (e.g., valve 584, 586, 588, 590,respectively) associated with the outlet port (e.g., port 518, 524, 538,545, respectively) of the respective pneumatic chamber is opened topermit the gas to be transferred to the next downstream chamber as thegas is being compressed.

As shown in FIG. 5G, the pneumatic pistons 520, 540 and the hydraulicpistons 551, 561 have completed their second stroke and each piston 520,540, 551, 561 is now back in their first position (see, for example,FIG. 5A). In some embodiments, the pistons 520, 540, 551, 561 moveconcurrently with each other and can have the same stroke time. In otherwords, in some embodiments, the pistons 520, 540, 551, 561 can beginand/or end their respective strokes at the same time. In someembodiments, the pistons 520, 540, 551, 561 can have the same stroketime (e.g., three (3) seconds per stroke) but one or more of the pistons520, 540, 551, 561 start their stroke at different times. In otherembodiments, the timing of one or more of the pistons 520, 540, 551, 561can vary. For example, in some embodiments, the first working pneumaticpiston 520 can have a stroke time (i.e., the time it takes for piston520 to move from its first position to its fourth position) ofapproximately five (5) seconds, the second working pneumatic piston 540can have a stroke time of approximately four (4) seconds, and the firstand second working hydraulic pistons 551, 561 can have a stroke time ofapproximately three (3) seconds. Stroke times can vary, for example,based on the size and/or operation of the cylinders and/or pistons.

Referring to FIGS. 6A-6G, the compression/expansion device 500 isillustrated in first, second, third, fourth, fifth, sixth and seventhconfigurations, respectively, of an expansion mode or cycle. As shown inFIG. 6A, in the first configuration of the expansion mode, the valves580, 586, 588, 591, 595, 597, 599 are opened. The first and secondworking hydraulic pistons 551, 561 are in their fourth position withintheir respective hydraulic cylinders 550, 560 such that the volume ofthe first hydraulic chamber 552 is greater than the volume of the secondhydraulic chamber 562, and the third hydraulic chamber 562 is greaterthan the volume of the fourth hydraulic chamber 564. The valve 599between the fourth hydraulic chamber 564 and the liquid storagestructure 575 is opened. In this manner, the fourth hydraulic chamber564 is fluidically coupled to the liquid storage structure 575 such thata first volume of fluid can flow from the liquid storage structure 575to the fourth hydraulic chamber 564 via the first fluid port 523. Thevalve 591 between the first hydraulic chamber 553 and the liquid storagestructure 575 is also opened, and the first hydraulic chamber 553 isfluidically coupled the liquid storage structure 575 such that fluidfrom the first hydraulic chamber 553 can flow from the first hydraulicchamber 553 to the liquid storage structure 575. The valve 597 betweenthe third hydraulic chamber 562 and the fourth pneumatic chamber 534 isopened such that the third hydraulic chamber 562 is fluidically coupledto the fourth pneumatic chamber 534, and a second volume of liquid canflow from the third hydraulic chamber 562 to the fourth pneumaticchamber 534.

The second working pneumatic piston 540 is in its fourth position withinthe second pneumatic cylinder 530 such that the volume of the thirdpneumatic chamber 532 is less than the volume of the fourth pneumaticchamber 534. The valve 588 between the compressed gas storage chamber504 and the third pneumatic chamber 532 is opened. In this manner, thecompressed gas storage chamber 504 is fluidically coupled to the thirdpneumatic chamber 532 such that a first mass of compressed gas at afirst pressure can flow from the compressed gas storage chamber 504 intothe third pneumatic chamber 532 via the third fluid port 538. In someembodiments, a second mass of compressed gas at a second pressure iscontained in the fourth pneumatic chamber 534. The valve 586 between thefourth pneumatic chamber 534 and the second pneumatic chamber 514 isopened. In this manner, the fourth pneumatic chamber 534 is fluidicallycoupled to the second pneumatic chamber 512 such that the second mass ofcompressed gas and/or the second volume of liquid can flow from thefourth pneumatic chamber (via its first fluid port 542) to the secondpneumatic chamber (via its second fluid port 524) at the secondpressure.

The first working pneumatic piston 520 is in its fourth position withinthe first pneumatic cylinder 510 such that the volume of the firstpneumatic chamber 512 is greater than the volume of the second pneumaticchamber 514. The valve 695 between the second pneumatic chamber 514 andthe second hydraulic chamber 554 is opened. In this manner, the secondpneumatic chamber 514 is fluidically coupled to the second hydraulicchamber 554 such that a third volume of fluid (e.g., including thesecond volume of liquid or at least a portion thereof) can flow from thesecond pneumatic chamber 514 to the second hydraulic chamber 554. Athird mass of compressed gas at a third pressure can be contained in thefirst pneumatic chamber 512. The valve 580 between the first pneumaticchamber 512 and the gas source 502 is opened, and thus the firstpneumatic chamber 512 is fluidically coupled to the gas source 502 suchthat the third mass of compressed gas can flow from the first pneumaticchamber 512 via the first fluid port 516 to the gas source 502 at thethird pressure.

Referring now to FIG. 6B, the second working hydraulic piston 561 is inits third position. The valves 599 and 597 remain open so that the thirdand fourth hydraulic chambers 562, 564 are fluidically coupled to thefourth pneumatic chamber 534 and the liquid storage structure 575,respectively. The second working hydraulic piston 561 is moved by thethird hydraulic actuator 576 in the fourth direction to its secondposition (see, e.g., FIG. 6C), and to its first position (see, e.g.,FIG. 6D), thus completing a first stroke in the expansion mode. Movementof the second working hydraulic piston 561 in the fourth directioncauses the first volume of liquid to be drawn into the fourth hydraulicchamber 564, and the second volume of liquid to be discharged from thethird hydraulic chamber 562 into the fourth pneumatic chamber 534. Insome embodiments, the liquid flowing into and out of the third andfourth hydraulic chambers 562, 564 is relatively warmer than the fluidflowing into and out of the first and second hydraulic chambers 552,554. The warmed liquid can be, for example, the liquid warmed during thecompression mode and stored (or harvested) in the liquid storagestructure 575. By reintroducing this warmed liquid into the device 500,the system is, in essence, recycling the energy it previously producedduring the compression. In this manner, it may not be necessary for thesystem to exert more energy during the expansion mode to warm the gas asit expands. For example, in some embodiments, no external heatingdevices or mechanisms (e.g., burning fuels) are needed to heat thegas—the system can use the previously-produced heat that was absorbed bythe liquid. In other embodiments, however, at least a portion of thewarmed liquid is liquid injected back into the system after being warmedby an external heating device(s) or mechanism(s).

As shown in FIG. 6B, when the first mass of compressed gas is introducedinto the third pneumatic chamber 532, the first mass of compressed gasis permitted to expand within the third pneumatic chamber 532. The valve588 between the compressed gas storage chamber 504 and the thirdpneumatic chamber 532, which was previously open in FIG. 6A, is closedin the second configuration shown in FIG. 6B to prevent an additionalamount of compressed gas from flowing into the third pneumatic chamber532 and to prevent flow of the first mass of compressed gas back intothe compressed gas storage chamber 504. The expanding first mass ofcompressed gas exerts a force on the second working pneumatic piston 540sufficient to move the second working piston in the second direction toits third position (shown here in FIG. 6B), to its second position (see,e.g., FIG. 6C), and to its first position (see, e.g., FIG. 6D), thuscompleting a first stroke in the expansion mode. After being permittedto expand in the third pneumatic chamber 532, the first mass ofcompressed gas has a fourth pressure lower than the first pressure.Movement of the second working pneumatic piston 540 in the seconddirection causes the second hydraulic actuator 574 to displace a firstvolume of hydraulic fluid.

Movement of the second working pneumatic piston 540 in the seconddirection also helps transfer the second mass of compressed gas at thesecond pressure from the fourth pneumatic chamber 534 to the secondpneumatic chamber 514. In some embodiments, however, before the secondmass of compressed gas is transferred, the second volume of liquid isintroduced into the fourth pneumatic chamber 534 to warm up the secondmass of compressed gas. In general, as gas expands and its pressuredecreases, the temperature of the gas decreases. This can lower thegas's ability to produce energy (i.e., to move the piston 540 togenerate electricity). Energy production can be increased, however, bywarming the gas prior to or during its expansion. Thus, the secondvolume of liquid is introduced into the fourth pneumatic chamber 534 towarm the second mass of compressed gas, which was expanded once in thefourth pneumatic chamber 534 and will be expanded again in the secondpneumatic chamber 514, to increase the energy production of the gas. Aspreviously discussed, in some embodiments, the second volume of liquidwas previously warmed during the compression process and stored withinthe liquid storage structure 575, and is now being re-introduced intothe device 500.

The second volume of liquid can be transferred from the fourth pneumaticchamber 534 to the second pneumatic chamber 514 along with the secondmass of compressed gas. The second mass of compressed gas is allowed toexpand further within the second pneumatic chamber. In some embodiments,the second volume of liquid continues to release heat in the secondpneumatic chamber 514 to warm the second mass of compressed gas as itcontinues to expand in the second pneumatic chamber 514. The expandingsecond mass of compressed gas exerts a force on the first workingpneumatic piston 520 to move the first working piston in the thirddirection from its third position (shown here in FIG. 6B), to its secondposition (see, e.g., FIG. 5C) and to its first position (see, e.g., FIG.5D), thus completing a first stroke in the expansion mode. After beingpermitted to expand in the second pneumatic chamber 514, the second massof compressed gas has a fifth pressure lower than the second pressure.

Movement of the first working pneumatic piston 520 in the thirddirection causes the first hydraulic actuator 572 to displace a secondvolume of hydraulic fluid. Movement of the first working pneumaticpiston 520 in the third direction also reduces the volume of the firstpneumatic chamber 512 and helps to transfer the third mass of compressedgas at the third pressure from the first pneumatic chamber 612 to thegas source 502. In some embodiments, the third pressure is substantiallyequal to the atmospheric pressure outside the gas source 502 (e.g., 1bar).

As shown in FIG. 6B, the first working hydraulic piston 551 is in itsthird position. The valves 591 and 595 remain open so that the first andsecond hydraulic chambers 552, 554 are fluidically coupled to the liquidstorage structure 575 and the second pneumatic chamber 524,respectively. The first working hydraulic piston 551 is moved with thesecond working hydraulic piston 561 in the fourth direction from itsthird position to its second position (see, e.g., FIG. 6C), and to itsfirst position (see, e.g., FIG. 6D), thus completing a first stroke inthe expansion mode. Movement of the first working hydraulic piston 551in the fourth direction causes a third volume of liquid (e.g., includingat least a portion of the second volume of liquid) to be drawn into thesecond hydraulic chamber 554 from the second pneumatic chamber 514, anda fourth volume of liquid to be discharged from the first hydraulicchamber 562 into the liquid storage structure 575.

By the time the third volume of liquid exits the device 500 and isreceived in the second hydraulic chamber, it is cooler than the secondvolume of liquid when it entered the device 500. In some embodiments,the liquid storage structure 575 is configured to store the warm liquiddispensed to the second hydraulic cylinder 560 and the cool liquidreceived from the first hydraulic cylinder 550 without one liquidsubstantial affecting the temperature of the other liquid. For example,in some embodiments, the liquid storage structure 575 can be dividedinto two portions that are fluidically and/or thermally isolated fromone another. One portion of the structure 575 can hold the cooler liquidand the other portion can hold the warmer liquid. In other embodiments,the liquid storage structure 575 can include a first tank that containsthe cooler liquid and a second, separate, tank that contains the warmerliquid.

In some embodiments, the force of the third volume of liquid enteringthe second hydraulic chamber 554 is sufficient to move the first andsecond working hydraulic pistons 551, 561 in the fourth direction. Asdiscussed above, in such embodiments, the third hydraulic actuator 576only exerts a force on the hydraulic pistons 551, 561 sufficient toovercome the hydraulic head and/or frictional losses in order to movethe hydraulic pistons 551, 561 in the fourth direction. In someembodiments, as discussed above, the fluid pressure produced by thethird volume of liquid entering the second hydraulic chamber 554 is theprimary force acting on the hydraulic pistons 551, 561, and thehydraulic force exerted by the third hydraulic actuator 576 can be asecondary force. In other embodiments, as discussed above, the hydraulicforce exerted by the third hydraulic actuator 576 is the primary forceand the fluid pressure exerted by the liquid entering the secondhydraulic chamber 554 is the secondary force acting on the first andsecond working hydraulic pistons 551, 561.

Referring now to FIG. 6C, the valves 580, 586, 591, 595, 597 and 599remain open while valve 588 remains closed to prevent any gas in thethird pneumatic chamber 632 from flowing back into the gas storagechamber 504. The first mass of compressed gas continues to expand in thethird pneumatic chamber 632 and move the second working pneumatic piston540 in the second direction. Likewise, the second mass of compressed gascontinues to flow from the fourth pneumatic chamber 634 to the secondpneumatic chamber 614 where it continues to expand and move the firstworking pneumatic piston 520 in the third direction. The first andsecond working pneumatic pistons 520, 540 are shown in their respectivesecond positions. The first and second hydraulic pistons 551, 561 arealso shown in their second positions. The first and second hydraulicpistons 551, 561 continue to move in the fourth direction and operate inthe same manner described above with respect to FIG. 6B.

Turning now to FIG. 6D, the previously-opened valves 580, 586, 591, 595,597, 599 are closed and valves 582, 584, 590, 593, 594, 596, 598 areopened. The first and second working hydraulic pistons 551, 561 havecompleted their first stroke of the expansion mode and are in theirfirst position. As such, the first and second working hydraulic pistons551, 561 are in position to begin their second stroke of the expansionmode. At this point during the cycle, the fourth volume of fluid hasbeen at least partially or fully discharged from the first hydraulicchamber 552. At valve 596, the fourth hydraulic chamber 562 isfluidically coupled to the third pneumatic chamber 532 such that thewarmed first volume of liquid (or at least a portion thereof) can flowfrom the fourth hydraulic chamber 562 to the third pneumatic chamber532. At valve 597, the third hydraulic chamber 564 is fluidicallycoupled to the liquid storage structure 575 such that a fifth volume ofliquid, which is warm, can flow from the liquid storage structure 575 tothe third hydraulic chamber 564. At valve 593, the second hydraulicchamber 554 is coupled to the liquid storage structure 575 such that thethird volume of liquid (or at least a portion thereof), which isrelatively cooler than the warm first volume of liquid, can flow fromthe second hydraulic chamber 554 to the liquid storage structure 575. Atvalve 594, the first hydraulic chamber 552 is fluidically coupled to thefirst pneumatic chamber 512 such that liquid, which is also relativelycooler than the warm first volume of liquid, can flow from the firstpneumatic chamber 512 to the first hydraulic chamber 552.

The second working pneumatic piston 540, having completed its firststroke, is in its first position. At this point in the cycle, the secondmass of compressed gas has been at least partially or fully dischargedfrom the fourth pneumatic chamber 534 into the second pneumatic chamber514. As shown in FIG. 6D, the third pneumatic chamber 532 is fluidicallycoupled to the first pneumatic chamber 512 such that the first mass ofcompressed gas can be discharged from the third pneumatic chamber 532 tothe first pneumatic chamber 512 at the fourth pressure. The firstworking pneumatic piston 520, having also completed its first stroke, isin its first position. The valve 580 between the first pneumatic chamber512 and the gas source 502 is closed to fluidically isolate the firstpneumatic chamber from the gas source 502. The valve 582 between thesecond pneumatic chamber 514 and the gas source 502 is opened, and thusthe second pneumatic chamber 514 is fluidically coupled to the gassource 502 such that the second mass of gas can be discharged from thesecond pneumatic chamber 514 to the gas source at the fifth pressure.

Because valve 590 is opened, the compressed gas storage chamber 504 isfluidically coupled to the fourth pneumatic chamber 534 such that afourth mass of compressed gas can flow from the storage chamber 504 tothe fourth pneumatic chamber 534. The fourth mass of compressed gas isdischarged from the compressed gas storage chamber 504 to the fourthpneumatic chamber 534 at a sixth pressure. As the fourth mass of gasenters and expands in the fourth pneumatic chamber 534, it exerts aforce on the second working pneumatic piston 540 thereby moving thesecond working piston 540 in the third direction from its first position(shown here in FIG. 6D) to its second, third and fourth positions,respectively.

As the second working piston 540 is moved in its third direction, thefirst mass of compressed gas is discharged from the third pneumaticchamber 532 to the first pneumatic chamber 512 at the fourth pressure.In some embodiments, however, before being discharged to the firstpneumatic chamber 512, a first volume of liquid (which, for example, waspreviously warmed during the compression process) is introduced into thethird pneumatic chamber 532 to warm the first mass of compressed gas.The first volume of liquid can be transferred into the first pneumaticchamber 512 along with the first mass of compressed gas.

In the first pneumatic chamber 512, the first mass of compressed gas isallowed to expand and thereby exert a force on the first workingpneumatic piston 520 to move the first working piston 520 in the seconddirection to its first position (shown here in FIG. 6D). As the firstworking pneumatic piston 520 is moved in the second direction, thesecond mass of gas is discharged from the second pneumatic chamber 514to the gas source 502 at the fifth pressure. In some embodiments, thefifth pressure is substantially equal to the atmospheric pressureoutside the gas source 502. A sixth volume of liquid (e.g., including atleast a portion of the first volume of liquid) can also be dischargedfrom the first pneumatic chamber 512 to the first hydraulic chamber 552as the first working pneumatic piston 520 moves in the second direction.

The first hydraulic piston 551, which is shown in its first position, ismoved in the first direction with the second hydraulic piston 561. Asthe first working hydraulic piston 551 moves in the first direction, thesixth volume of liquid is drawn into the first hydraulic chamber 552from the first pneumatic chamber 512, and the third volume of fluid (orat least a portion thereof) is discharged from the second hydraulicchamber 554 into the liquid storage structure 575. As discussed above,the force of the sixth volume of liquid entering the first hydraulicchamber 552 can be sufficient to move the first hydraulic piston 551 inthe first direction with limited assistance from the third hydraulicactuator 576. In some embodiments, the fluid force produced by the sixthvolume of liquid entering the first hydraulic chamber 552 is the primaryforce acting on the first hydraulic piston 551, and the and hydraulicforce exerted by the third hydraulic actuator 576 is the secondaryforce. In other embodiments, the hydraulic force is the primary forceand the fluid force is the secondary force.

Referring now to FIG. 6E, the second working hydraulic piston 561 is inits second position. The valves 598 and 596 remain open so that thethird and fourth hydraulic chambers 562, 564 continue to be fluidicallycoupled to the liquid storage structure 575 and the third pneumaticchamber 532, respectively. The second working hydraulic piston 561continues to move in the first direction with the first workinghydraulic piston 551, and each hydraulic piston 551, 561 operates in thesame manner discussed above.

The valve 588 between the compressed gas storage chamber 504 and thethird pneumatic chamber 532, which was previously open in FIG. 6D, isclosed to prevent an additional amount of compressed gas from flowinginto the chamber 504 and to prevent flow of the fourth mass ofcompressed gas back into the compressed gas storage chamber 504. Thefourth mass of compressed gas continues to expand within the fourthpneumatic chamber 534 in the manner described above.

As previously discussed, the expanding fourth mass of compressed gasexerts a force on the second working pneumatic piston 540 sufficient tomove the second working piston in the third direction to its third andfourth positions, thus completing a second stroke in the expansion mode.After being permitted to expand in the fourth pneumatic chamber 534, thefourth mass of compressed gas has a seventh pressure lower than thesixth pressure. Movement of the second working pneumatic piston 540 inthe third direction causes the second hydraulic actuator 574 to displacea third volume of hydraulic fluid.

Movement of the second working pneumatic piston 540 in the thirddirection also helps transfer the first mass of compressed gas at thefourth pressure from the third pneumatic chamber 532 to the firstpneumatic chamber 514. Before the first mass of compressed gas istransferred, however, the first volume of liquid is introduced into thethird pneumatic chamber 532 from the fourth hydraulic chamber 564 towarm the first mass of compressed gas. The second volume of liquid canbe transferred from the third pneumatic chamber 532 to the firstpneumatic chamber 512 with the first mass of compressed gas. The firstmass of compressed gas is permitted to expand further within the firstpneumatic chamber 512 and, in some embodiments, the first volume ofliquid can continue to release and transfer heat to the gas during thistime. The expanding first mass of gas exerts a force on the firstworking pneumatic piston 520 to move the first working piston in thesecond direction to its third and fourth positions, thus completing asecond stroke in the expansion mode. After being permitted to expand inthe second pneumatic chamber 514, the first mass of compressed gas hasan eighth pressure lower than the fourth pressure. Movement of the firstworking pneumatic piston 520 in the second direction causes the firsthydraulic actuator 572 to displace a fourth volume of hydraulic fluid.Movement of the first working pneumatic piston 520 in the seconddirection also reduces the volume of the second pneumatic chamber 514and helps to transfer the second mass of compressed gas at the fifthpressure from the second pneumatic chamber 514 to the gas source 502.

As shown in FIG. 6E, the first working hydraulic piston 551 is in itssecond position. The valves 593 and 594 remain open so that the firstand second hydraulic chambers 552, 554 are fluidically coupled to thefirst pneumatic chamber 512 and the liquid storage structure 575,respectively. Movement of the first working hydraulic piston 551 in thefirst direction causes the sixth volume of liquid (e.g., including atleast a portion of the first volume of liquid) to be drawn into thefirst hydraulic chamber 552 from the first hydraulic chamber 512, andthe third volume of liquid (or at least a portion thereof) to bedischarged from the second hydraulic chamber 554 into the liquid storagestructure 575. The first working hydraulic piston 551 is moved with thesecond working hydraulic piston 561 in the first direction to its thirdand fourth positions, thus completing a second stroke in the expansionmode.

Referring now to FIG. 6F, the valves 582, 584, 593, 594, 596 and 598continue remain open while valve 590 continues remains closed to preventany gas in the fourth pneumatic chamber 634 from flowing back into thegas storage chamber 504. The fourth mass of compressed gas continues toexpand in the fourth pneumatic chamber 634 and move the second workingpneumatic piston 540 in the third direction to its third position, shownhere. Likewise, the first mass of compressed gas continues to flow fromthe third pneumatic chamber 532 to the first pneumatic chamber 512 whereit is further permitted to expand. This expansion forces the firstpneumatic piston 520 to move in the second direction to its thirdposition, shown here. The first and second hydraulic pistons 551, 561are also in their third positions. Movement of the first and secondhydraulic pistons 551, 561 in the first direction continues to displaceliquid in the manner discussed above.

Referring now to FIG. 6G, the hydraulic pistons 551, 561 and thepneumatic pistons 520, 540 are each in their respective fourthpositions, having completed a second stroke in the expansion mode. Inthis position, the first volume of liquid has been at least partially orfully discharged from the fourth hydraulic chamber 564 and into thedevice 500, and the third volume of liquid has been at least partiallyor fully discharged from the second hydraulic chamber 552 and into theliquid storage structure 575.

The fourth mass of gas has expanded within the fourth pneumatic chamber534, thereby moving the second working pneumatic piston 540 in the thirddirection to its fourth position. In completing its second stroke, thesecond working pneumatic piston 540 moved in the third direction toincrease the volume of the fourth pneumatic chamber 534 and decrease thevolume of the third pneumatic chamber 532. Additionally, the secondworking pneumatic piston 540, having moved in the third direction fromits first position to its fourth position (i.e., its second stroke inthe expansion mode), caused the second hydraulic actuator 574 todisplace a third volume of hydraulic fluid.

The first mass of compressed gas and the first volume of fluid have beendischarged to the first pneumatic chamber 512 from the third pneumaticchamber 532 and the valve 584 therebetween is closed. The first mass ofcompressed gas has expanded within the first pneumatic chamber 512, andnow has an eighth pressure lower than the fourth pressure. The expandingfirst mass of gas moved the first working pneumatic piston 520 in thesecond direction to its fourth position. In completing its secondstroke, the first working pneumatic piston 520 moved in the seconddirection to increase the volume of the first pneumatic chamber 512 anddecrease the volume of the second pneumatic chamber 514. Additionally,the first working pneumatic piston 520, having moved in the seconddirection from its fourth position to its first position (i.e., itssecond stroke), caused the first hydraulic actuator 572 to displace afourth volume of hydraulic fluid. The second stroke of the first workingpneumatic piston 520 can be concurrent with, or substantiallysimultaneous with, the second stroke of the second working pneumaticpiston 540. As shown in FIG. 6G, the second mass of compressed gas hasbeen discharged from the second pneumatic chamber 514 to the gas source502 at the fifth pressure.

The displacement of each volume of fluid (e.g., the first, second,third, or fourth volumes of fluid) by the first and second hydraulicactuators 572, 574 generates hydraulic power. In embodiments where thefirst and second hydraulic pistons 551, 561 are moved using hydraulicforce (as described above), the third hydraulic actuator 576 can alsodisplace a volume of fluid to generate hydraulic power. The hydrauliccontroller 570 controls distribution of the hydraulic power using, forexample, software programmed to control a system of valves (not shown)within the hydraulic controller. The hydraulic controller 570 cancontrol distribution of the hydraulic power to a pump/motor 571, whichis configured to convert the hydraulic power into mechanical power. Thepump/motor 571 is configured to transmit the mechanical power to amotor/generator 578. The motor/generator 578 is configured to convertthe mechanical power to electrical power, which can then be transmittedto a power grid. The expansion mode, or cycle, can be continued orrepeated as desired to convert energy stored in the form of compressedgas into electrical energy.

Although the compression/expansion devices (e.g., devices 100, 200, 300,500) have been illustrated and described herein as including twopneumatic cylinders (e.g., cylinders 110 and 130, 210 and 230, 310 and330, 510 and 530, respectively), in some embodiments, acompression/expansion device includes more than two pneumatic cylinders.Similarly, although the lock pumps (e.g., lock pumps 490, 590) have beenillustrated and described herein as including two hydraulic cylinders(e.g., cylinders 450 and 460, 550 and 560, respectively), in someembodiments, a lock pump includes more than two hydraulic cylinders.

Although the lock pumps (e.g., lock pumps 490, 590) have beenillustrated and described as including a first hydraulic cylinder (e.g.,first hydraulic cylinders 450, 550) and a second hydraulic cylinder(e.g., second hydraulic cylinders 460, 560), in some embodiments, a lockpump includes hydraulic chambers differently configured. For example, insome embodiments a lock pump can include a single vessel divided into afirst hydraulic portion and a second hydraulic portion, with the firstand second hydraulic portions each being divided by working pistons intotwo hydraulic chambers. Operation of such a system can be similar inmany respects to operation of lock pump 590.

A system for compression and/or expansion of gas can include anysuitable combination of systems (e.g., system 100, 200, 300, 500), orportions thereof, described herein. For example, in some embodiments,such a system can include any combination of system 300 (described withreference to FIG. 3), and system 500 (described with reference to FIGS.5 and 6). For example, a system can include two or more pneumaticcylinders in an in-line configuration and two or more pneumaticcylinders in a stacked configuration. Additionally, a system can includeone, two, three, four, or more cylinders per stage ofcompression/expansion. A liquid management system can include anysuitable combination of systems (192, 392, 592), or portions thereof(e.g., lock pump 490), described herein. In some embodiments, a liquidmanagement system can include two or more hydraulic cylinders in anin-line configuration and two or more hydraulic cylinders in a stackedconfiguration. Additionally, a liquid management system can include one,two, three, four, or more hydraulic cylinders per stage ofcompression/expansion. The number of hydraulic cylinders can correspond,for example, to the number of pneumatic cylinders in the compressionand/or expansion system. The liquid management system can operate withany compression and/or expansion system (e.g., system 100, 200, 300,500) described herein.

Although the liquid management system 592 is illustrated and describedherein as including the hydraulic actuator 576, in other embodiments,the liquid management system 592 does not include this actuator. Rather,the fluid pressure discussed above is the only force acting on thepistons 551, 561 to move the pistons 551, 561. As such, the timing andmovement of the pistons 551, 561 will be dependent, in part, on thepneumatic pistons 520, 540. In some such embodiments, it is notnecessary that the first and second hydraulic pistons 551, 561 becoupled together, for example, via a piston rod or other like connectingrod. Rather, the hydraulic pistons 551, 561 can move in their respectivecylinders 550, 560 independently of each other. The hydraulic pistons551, 561 in this embodiment can, for example, function as dividers (orother moveable barrier/separator) within their respective cylinders 550,560 as opposed to pistons.

The devices and systems described herein can be implemented in a widerange of sizes and operating configurations. Said another way, thephysics and fluid mechanics of the system do not depend on a particularsystem size. For example, systems in the power range of 2 to 8 MW aretechnically and economically achievable. This estimated power rangeresults from a system design constrained to use current commerciallyavailable components, manufacturing processes, and transportationprocesses. Larger and/or smaller system power may be preferred if thedesign uses a greater fraction of custom, purpose-designed components.Moreover, system power also depends on the end-use of the system. Saidanother way, the size of the system may be affected by whether thesystem is implemented as a compressor/expander, as may be the case in aCAES application, or whether the system is implemented as an expander,as may be the case in a natural gas distribution system component, or asa compressor, as may be the case in a carbon dioxide sequestrationapplication.

As noted above, devices and systems for the compression/expansion ofgas, according to embodiments, are configured for grid scale energystorage. As such, a pneumatic cylinder (or pneumatic portion of avessel) can be any suitable size for achieving gas compression for gridscale energy storage and/or gas expansion for grid scale energy usage.For example, in some embodiments, a pneumatic cylinder for the firststage of compression (and/or a second or later stage of expansion) canbe about 10.3 meters in height and about 3.5 meters in diameter. Inanother example, a pneumatic cylinder for the second stage ofcompression (and/or a first or non-late stage of expansion) can be about10 meters in height and about 1.6 meters in diameter. In someembodiments, a system includes a cylinder (or vessel) up to about 1.6meters, which is within current technology capabilities for precisionmachining (e.g., honing and chroming) an inner surface of the cylinderto produce a good seal between a working piston and the inner surface ofthe cylinder. In some embodiments, a system includes a cylinder (orvessel) larger than about 1.6 meters, which exceeds current technologycapabilities for precision machining. Accordingly, such a largercylinder can include a rolling piston seal, such as that described inU.S. Patent App. No. 61/420,505, to Ingersoll et al., filed Dec. 7,2010, entitled “Compressor and/or Expander Device with Rolling PistonSeal,” (“the '505 application”) the disclosure of which is incorporatedherein by reference in its entirety.

Additionally, a compression/expansion device according to an embodimentcan be configured to compress a volume of gas from a first pressure to asecond higher pressure which will occupy a lower volume. For example, insome embodiments, a compression/expansion device can be configured toreceive about 15,000 liters to about 20,000 liters of gas at a firstpressure (i.e., the inhale volume of the first-stage cylinder atstandard atmospheric pressure) at the first stage of compression. Forexample, the compression/expansion device can be configured to compressabout 16,000 liters of gas at the first stage of compression. In someembodiments, the compressor/expander device can be configured tocompress the inhale volume of the first-stage cylinder to a pressureabout 6 to 10 times its original pressure, thus reducing the volumeoccupied by that mass of gas to about 2,000-2,500 liters (i.e., theinhale volume of the second-stage cylinder). In some embodiments, thecompressor/expander device can be configured to receive about 2,350liters of gas at a second pressure, higher than the first pressure, atthe second stage of compression. In other words, a first pneumaticcylinder of the compression/expansion device can be configured toreceive an inhale volume of about 16,000 liters of gas at a firstpressure for the first stage of compression and compress the gas duringthe first stage to about 2,350 liters of gas at a second pressure. Asecond pneumatic cylinder of the compression/expansion device can beconfigured to receive an inhale volume of the 2,350 liters of gas at thesecond pressure from the first pneumatic cylinder and compress the gasto a third pressure, higher than the second pressure. As such, in thisexample, the first stage of the compressor/expander device can becharacterized as being configured to achieve about a 1:6.8 compressionratio.

The compression ratio of the second stage of the compressor/expanderdevice can be characterized as the volume available to contain a mass ofgas when the piston is at bottom dead center and the volume available tocontain the mass of gas when the piston is at top dead center. In theexample described above where the second pneumatic cylinder isconfigured to receive an inhale volume of the 2,350 liters of gas at thesecond pressure, the volume available to contain a mass of gas when thepiston is at bottom dead center is 2,350. In some embodiments the volumeavailable to contain the mass of gas when the piston is at top deadcenter is about 178 liters. As such, in this example, the second stageof the compressor/expander device can be characterized as beingconfigured to achieve about a 6.8:90 compression ratio. The second stageof the compressor/expander device can be configured to operate atdifferent pressure ratios to discharged compressed gas to a third stageand/or a compressed gas storage structures by changing the stroke of thepiston (i.e., changing the volumetric ratio between bottom dead centerand top dead center to define the pressure ratio in the second stage).

Devices and systems used to compress and/or expand a gas can beconfigured to operate in a compression mode to compress a gas in excessof 700 bar. In some embodiments, a compression/expansion device isconfigured to compress a gas through two or three stages of compression.For example, the device can be configured to achieve a gas pressureratio of 1:10 at a first stage of compression, and 10:250 at a secondstage of compression. In another example, the device can be configuredto achieve a gas pressure ratio of 1:6 at the first stage ofcompression, 6:90 at the second stage of compression, and, optionally,90:250 at a third stage of compression. In yet another example, thedevice can be configured to compress the gas such that the pressure ofthe gas following the second stage of compression is 15 times greaterthan the pressure of the gas following the first stage of compress, thusachieving a pressure ratio of 1:15.

Devices and systems used to compress and/or expand a gas can beconfigured to operate in an expansion mode to expand a gas such that thecompressed gas from the compressed gas storage chamber has a pressureratio to the expanded gas of 250:1. In some embodiments, acompression/expansion device is configured to expand a gas through twoor three stages of expansion. For example, the device can be configuredto achieve a gas expansion ratio of 250:10 at a first stage ofexpansion, and 10:1 at a second stage of expansion. In another example,the device can be configured to achieve a gas pressure ratio of 90:9 atthe first stage of expansion, and 9:1 at the second stage ofcompression. In yet another example, the device can be configured toachieve a gas pressure ratio of 250:90 at a first stage of compression,90:6 or 90:9 at the second stage of compression, and, optionally 6:1 or9:1 at the third stage of compression.

Devices and systems used to compress and/or expand a gas, such as air,and/or to pressurize and/or pump a liquid, such as water, can releaseand/or absorb heat during, for example, a compression or expansioncycle. In some embodiments, one or more pneumatic cylinders can includea heat capacitor for transferring heat to and/or from the gas as it isbeing compressed/expanded, for example as described in the '679application, incorporated by reference above. For example, a heattransfer element can be positioned within the interior of a pneumaticcylinder of a compressor/expander device to increase the amount ofsurface area within the pneumatic cylinder that is in direct or indirectcontact with gas, which can improve heat transfer. In some embodiments,the heat transfer element can be a thermal capacitor that absorbs andholds heat released from a gas that is being compressed, and thenreleases the heat to a gas or a liquid at a later time. In someembodiments, the heat transfer element can be a heat transferring devicethat absorbs heat from a gas that is being compressed, and thenfacilitates the transfer of the heat outside of the pneumatic cylinder.

In another example, heat can be transferred from and/or to gas that iscompressed and/or expanded by liquid (e.g., water) within a pneumaticcylinder. A gas/liquid or gas/heat element interface may move and/orchange shape during a compression and/or expansion process in apneumatic cylinder. This movement and/or shape change may provide acompressor/expander device with a heat transfer surface that canaccommodate the changing shape of the internal areas of a pneumaticcylinder in which compression and/or expansion occurs. In someembodiments, the liquid may allow the volume of gas remaining in apneumatic cylinder after compression to be nearly eliminated orcompletely eliminated (i.e., zero clearance volume).

A liquid (such as water) can have a relatively high thermal capacity ascompared to a gas (such as air) such that a transfer of an amount ofheat energy from the gas to the liquid avoids a significant increase inthe temperature of the gas, but only incurs a modest increase in thetemperature of the liquid. This allows buffering of the system fromsubstantial temperature changes. Said another way, this relationshipcreates a system that is resistant to substantial temperature changes.Heat that is transferred between the gas and liquid, or components ofthe vessel itself, may be moved from or to the pneumatic cylinderthrough one or more processes. In some embodiments, heat can be moved inor out of the pneumatic cylinder using mass transfer of the compressionliquid itself. In other embodiments, heat can be moved in or out of thepneumatic cylinder using heat exchange methods that transfer heat in orout of the compression liquid without removing the compression liquidfrom the pneumatic cylinder. Such heat exchangers can be in thermalcontact with the compression liquid, components of the pneumaticcylinder, a heat transfer element, or any combination thereof.Furthermore, heat exchangers may also use mass transfer to move heat inor out of the pneumatic cylinder. One type of heat exchanger that can beused to accomplish this heat transfer is a heat pipe as described in theCompressor and/or Expander Device applications and the '107 application,incorporated by reference above. Thus, the liquid within a pneumaticcylinder can be used to transfer heat from gas that is compressed (or togas that is expanded) and can also act in combination with a heatexchanger to transfer heat to an external environment (or from anexternal environment). Any suitable mechanism for transferring heat outof the device during compression and/or into the device during expansionmay be incorporated into the system.

In some embodiments, one or more hydraulic actuators of acompression/expansion device may incorporate “gear change” or “gearshift” features within a single stage of compression or expansion, orduring a cycle or stroke of the actuator, to optimize the energyefficiency of the hydraulic actuation. As used herein, the terms “gearchange” or “gear shift” are used to described a change in the ratio ofthe pressure of the hydraulic fluid in the active hydraulic actuatorchambers to the pressure of the gas in the working chamber actuated by(or actuating) the hydraulic actuator, which is essentially the ratio ofthe pressurized surface area of the working piston(s) to the net area ofthe pressurized surface area(s) of the hydraulic piston(s) actuating theworking piston(s). The term “gear” can refer to a state in which ahydraulic actuator has a particular piston area ratio (e.g., the ratioof the net working surface area of the hydraulic actuator to the workingsurface area of the working piston acting on, or being acted on by, thegas in a working chamber) at a given time period. Examples of suitablehydraulic actuators including “gear changes” or “gear shifts” aredescribed in the '724 application, incorporated by reference above.

The compressor/expander system can be configured for use with anysuitable compressed gas storage chamber, including, for example, anunderground storage structure (e.g., a pressure compensated saltcavern). Examples of suitable storage structures are described in U.S.Provisional App. No. 61/432,904 to Ingersoll et al., filed Jan. 14,2011, entitled “Compensated Compressed Gas Storage Systems,” thedisclosure of which is incorporated herein by reference in its entirety.The compressor/expander system can also be used with other types ofstorage, including, but not limited to, tanks, underwater storagevessels, and the like.

While various embodiments of the invention have been described above, itshould be understood that they have been presented by way of exampleonly, and not limitation. Where methods and steps described aboveindicate certain events occurring in certain order, those of ordinaryskill in the art having the benefit of this disclosure would recognizethat the ordering of certain steps may be modified and that suchmodifications are in accordance with the variations of the invention.Additionally, certain of the steps may be performed concurrently in aparallel process when possible, as well as performed sequentially asdescribed above. Additionally, certain steps may be partially completedbefore proceeding to subsequent steps. The embodiments have beenparticularly shown and described, but it will be understood that variouschanges in form and details may be made.

For example, although various embodiments have been described as havingparticular features and/or combinations of components, other embodimentsare possible having any combination or sub-combination of any featuresand/or components from any of the embodiments described herein. Forexample, although the device 201 is depicted as having a singlepneumatic cylinder for the first stage of compression, in someembodiments, the device can include two, three, or more pneumaticcylinders configured to operate the first stage of compression. Inanother example, although the devices 200, 300, 400, 500, 600 aredepicted as being configured for fluid communication with a singlecompressed gas storage chamber, in some embodiments, the devices 200,300, 400, 500, 600 be configured to be fluidically coupleable to anynumber of compressed gas storage chambers. Similarly, although devices200, 300, 400, 500, 600 are depicted being fluidically coupleable to asingle gas source, in some embodiments, devices 200, 300, 400, 500, 600can be fluidically coupleable to any number of gas sources. The specificconfigurations of the various components can also be varied. Forexample, the size and specific shape of the various components can bedifferent than the embodiments shown, while still providing thefunctions as described herein.

1.-137. (canceled)
 138. An apparatus suitable for use in a compressedgas-based energy storage and recovery system, the apparatus comprising:a first hydraulic cylinder comprising a first working piston disposedtherein for reciprocating movement, the first working piston dividingthe first hydraulic cylinder into, and defining therewith, a firsthydraulic chamber and a second hydraulic chamber; a second hydrauliccylinder comprising a second working piston disposed therein forreciprocating movement, the second working piston dividing the secondhydraulic cylinder into, and defining therewith, a third hydraulicchamber and a fourth hydraulic chamber; and an actuator coupled to andconfigured to move the first working piston and the second workingpiston: a) in a first direction such that liquid contained in the firsthydraulic chamber and the third hydraulic chamber is discharged from thefirst hydraulic chamber and the third hydraulic chamber, and b) in asecond direction, opposite the first direction, such that liquidcontained in the second hydraulic chamber and the fourth hydraulicchamber is discharged from the second hydraulic chamber and the fourthhydraulic chamber.
 139. The apparatus of claim 138, wherein a combinedvolume of the first and second hydraulic chambers is substantially equalto a combined volume of the third and fourth hydraulic chambers. 140.The apparatus of claim 138, wherein a volume of the first hydrauliccylinder is not equal to a volume of the second hydraulic cylinder. 141.The apparatus of claim 138, wherein a volume of the first hydraulicchamber is substantially equal to a volume of the third hydraulicchamber at any given time.
 142. The apparatus of claim 138, wherein avolume of the second hydraulic chamber is substantially equal to avolume of the fourth hydraulic chamber at any given time.
 143. Theapparatus of claim 138, wherein a change in volume of the firsthydraulic chamber corresponds to a change in volume of the secondhydraulic chamber.
 144. The apparatus of claim 138, wherein a change involume of the first hydraulic chamber corresponds to a change in volumeof the third hydraulic chamber.
 145. The apparatus of claim 138, whereinthe first and second hydraulic cylinders are fluidically coupled to aliquid storage structure.
 146. The apparatus of claim 145, wherein theliquid storage structure is at least one of a storage vessel, a pond, atank, and a pool.
 147. The apparatus of claim 138, wherein the firsthydraulic cylinder comprises a first fluid port and a second fluid port,the second hydraulic cylinder comprises a third fluid port and fourthfluid port, and wherein the actuator moving the first and second workingpistons in the first direction causes: a) liquid contained within thefirst hydraulic chamber to be discharged from the first hydraulicchamber via the first fluid port, b) liquid to be drawn into the secondhydraulic chamber via the second fluid port, c) liquid contained withinthe third hydraulic chamber to be discharged from the third hydraulicchamber via the third fluid port, and d) liquid to be drawn into thefourth chamber via the fourth fluid port.
 148. The apparatus of claim138, wherein the first hydraulic cylinder comprises a first fluid portand a second fluid port, the second hydraulic cylinder comprises a thirdfluid port and fourth fluid port, and wherein the actuator moving thefirst and second working pistons in the second direction causes: a)liquid to be drawn into the first hydraulic chamber via the first fluidport, b) liquid contained within the second hydraulic chamber to bedischarged from the second hydraulic chamber via the second fluid port,c) liquid to be drawn into the third chamber via the third fluid port,and d) liquid contained within the fourth hydraulic chamber to bedischarged from the fourth hydraulic chamber via the fourth fluid port.149. The apparatus of claim 138, wherein the actuator is operable tomove the first working piston in phase with the second working piston.150. The apparatus of claim 138, wherein the actuator is furtherconfigured to move the first and second working pistons: a) in the firstdirection to reduce the volume of the first hydraulic chamber and thethird hydraulic chamber, and b) in the second direction to reduce thevolume of the second hydraulic chamber and the fourth hydraulic chamber.151. The apparatus of claim 138, wherein the actuator is selected fromthe group consisting of an electric motor and a hydraulic actuator. 152.The apparatus of claim 138, wherein the apparatus comprises at least oneadditional hydraulic cylinder.
 153. A method of controlling thermalefficiency of a compressed gas-based energy storage and recovery system,the system comprising: a first hydraulic cylinder comprising a firstworking piston disposed therein for reciprocating movement, the firstworking piston dividing the first hydraulic cylinder into, and definingtherewith, a first hydraulic chamber and a second hydraulic chamber; asecond hydraulic cylinder comprising a second working piston disposedtherein for reciprocating movement, the second working piston dividingthe second hydraulic cylinder into, and defining therewith, a thirdhydraulic chamber and a fourth hydraulic chamber; and an actuatorcoupled to the first working piston and the second working piston, themethod comprising: moving, using the actuator, the first and secondworking pistons: a) in a first direction such that liquid contained inthe first hydraulic chamber and the third hydraulic chamber isdischarged from the first hydraulic chamber and the third hydraulicchamber, and b) in a second direction, opposite the first direction,such that liquid contained in the second hydraulic chamber and thefourth hydraulic chamber is discharged from the second hydraulic chamberand the fourth hydraulic chamber.
 154. The method of claim 153, whereinthe first hydraulic cylinder comprises a first fluid port and a secondfluid port, the second hydraulic cylinder comprises a third fluid portand fourth fluid port, and wherein the method further comprises: a)discharging liquid contained within the first hydraulic chamber via thefirst fluid port, b) drawing liquid into the second hydraulic chambervia the second fluid port, c) discharging liquid contained within thethird hydraulic chamber via the third fluid port, and d) drawing liquidinto the fourth chamber via the fourth fluid port.
 155. The method ofclaim 153, wherein the first hydraulic cylinder comprises a first fluidport and a second fluid port, the second hydraulic cylinder comprises athird fluid port and fourth fluid port, and wherein the method furthercomprises: a) drawing liquid into the first hydraulic chamber via thefirst fluid port, b) discharging liquid contained within the secondhydraulic chamber via the second fluid port, c) drawing liquid into thethird chamber via the third fluid port, and d) discharging liquidcontained within the fourth hydraulic chamber via the fourth fluid port.156. The method of claim 153, further comprising moving, using theactuator, the first working piston in phase with the second workingpiston.
 157. The apparatus of claim 153, further comprising moving,using the actuator, the first and second working pistons: a) in thefirst direction to reduce the volume of the first hydraulic chamber andthe third hydraulic chamber, and b) in the second direction to reducethe volume of the second hydraulic chamber and the fourth hydraulicchamber.
 158. The method of claim 153, further comprising fluidicallycoupling the first and second hydraulic cylinders to a liquid storagestructure.